2.1.7 Problem 7

Internal problem ID [4082]
Book : Differential equations, Shepley L. Ross, 1964
Section : 2.4, page 55
Problem number : 7
Date solved : Wednesday, November 26, 2025 at 03:32:45 PM
CAS classification : [[_homogeneous, `class C`], _rational, [_Abel, `2nd type`, `class A`]]

Solved using first_order_ode_dAlembert

Time used: 0.245 (sec)

Solve

\begin{align*} x -2 y-3+\left (2 x +y-1\right ) y^{\prime }&=0 \\ \end{align*}

Let \(p=y^{\prime }\) the ode becomes

\begin{align*} x -2 y -3+\left (2 x +y -1\right ) p = 0 \end{align*}

Solving for \(y\) from the above results in

\begin{align*} \tag{1} y &= -\frac {\left (2 p +1\right ) x}{-2+p}-\frac {-p -3}{-2+p} \\ \end{align*}

This has the form

\begin{align*} y=x f(p)+g(p)\tag {*} \end{align*}

Where \(f,g\) are functions of \(p=y'(x)\). The above ode is dAlembert ode which is now solved.

Taking derivative of (*) w.r.t. \(x\) gives

\begin{align*} p &= f+(x f'+g') \frac {dp}{dx}\\ p-f &= (x f'+g') \frac {dp}{dx}\tag {2} \end{align*}

Comparing the form \(y=x f + g\) to (1A) shows that

\begin{align*} f &= \frac {-2 p -1}{-2+p}\\ g &= \frac {p +3}{-2+p} \end{align*}

Hence (2) becomes

\begin{equation} \tag{2A} p -\frac {-2 p -1}{-2+p} = \left (-\frac {2 x}{-2+p}+\frac {2 x p}{\left (-2+p \right )^{2}}+\frac {x}{\left (-2+p \right )^{2}}+\frac {1}{-2+p}-\frac {p}{\left (-2+p \right )^{2}}-\frac {3}{\left (-2+p \right )^{2}}\right ) p^{\prime }\left (x \right ) \end{equation}

The singular solution is found by setting \(\frac {dp}{dx}=0\) in the above which gives

\begin{align*} p -\frac {-2 p -1}{-2+p} = 0 \end{align*}

Solving the above for \(p\) results in

\begin{align*} p_{1} &=i\\ p_{2} &=-i \end{align*}

Substituting these in (1A) and keeping singular solution that verifies the ode gives

\begin{align*} y = i \left (-1+i+x \right )\\ y = -i x +i-1 \end{align*}

The general solution is found when \( \frac { \mathop {\mathrm {d}p}}{\mathop {\mathrm {d}x}}\neq 0\). From eq. (2A). This results in

\begin{equation} \tag{3} p^{\prime }\left (x \right ) = \frac {p \left (x \right )-\frac {-2 p \left (x \right )-1}{-2+p \left (x \right )}}{-\frac {2 x}{-2+p \left (x \right )}+\frac {2 x p \left (x \right )}{\left (-2+p \left (x \right )\right )^{2}}+\frac {x}{\left (-2+p \left (x \right )\right )^{2}}+\frac {1}{-2+p \left (x \right )}-\frac {p \left (x \right )}{\left (-2+p \left (x \right )\right )^{2}}-\frac {3}{\left (-2+p \left (x \right )\right )^{2}}} \end{equation}

This ODE is now solved for \(p \left (x \right )\). No inversion is needed.

The ode

\begin{equation} p^{\prime }\left (x \right ) = \frac {\left (-2+p \left (x \right )\right ) \left (p \left (x \right )^{2}+1\right )}{5 x -5} \end{equation}

is separable as it can be written as

\begin{align*} p^{\prime }\left (x \right )&= \frac {\left (-2+p \left (x \right )\right ) \left (p \left (x \right )^{2}+1\right )}{5 x -5}\\ &= f(x) g(p) \end{align*}

Where

\begin{align*} f(x) &= \frac {1}{5 x -5}\\ g(p) &= \left (-2+p \right ) \left (p^{2}+1\right ) \end{align*}

Integrating gives

\begin{align*} \int { \frac {1}{g(p)} \,dp} &= \int { f(x) \,dx} \\ \int { \frac {1}{\left (-2+p \right ) \left (p^{2}+1\right )}\,dp} &= \int { \frac {1}{5 x -5} \,dx} \\ \end{align*}

\[ \ln \left (\frac {\left (-2+p \left (x \right )\right )^{{1}/{5}}}{\left (p \left (x \right )^{2}+1\right )^{{1}/{10}}}\right )-\frac {2 \arctan \left (p \left (x \right )\right )}{5}=\ln \left (\left (x -1\right )^{{1}/{5}}\right )+c_1 \]

We now need to find the singular solutions, these are found by finding for what values \(g(p)\) is zero, since we had to divide by this above. Solving \(g(p)=0\) or

\[ \left (-2+p \right ) \left (p^{2}+1\right )=0 \]

for \(p \left (x \right )\) gives

\begin{align*} p \left (x \right )&=2\\ p \left (x \right )&=-i \end{align*}

Now we go over each such singular solution and check if it verifies the ode itself and any initial conditions given. If it does not then the singular solution will not be used.

Therefore the solutions found are

\begin{align*} \ln \left (\frac {\left (-2+p \left (x \right )\right )^{{1}/{5}}}{\left (p \left (x \right )^{2}+1\right )^{{1}/{10}}}\right )-\frac {2 \arctan \left (p \left (x \right )\right )}{5} &= \ln \left (\left (x -1\right )^{{1}/{5}}\right )+c_1 \\ p \left (x \right ) &= 2 \\ p \left (x \right ) &= -i \\ \end{align*}

Substituing the above solution for \(p\) in (2A) gives

\begin{align*} y &= -i \left (x -1-i\right ) \\ \end{align*}

Figure 2.21: Slope field \(x -2 y-3+\left (2 x +y-1\right ) y^{\prime } = 0\)

Summary of solutions found

\begin{align*} y &= i \left (-1+i+x \right ) \\ y &= -i x +i-1 \\ \end{align*}

Solved using first_order_ode_homog_type_maple_C

Time used: 0.524 (sec)

Solve

\begin{align*} x -2 y-3+\left (2 x +y-1\right ) y^{\prime }&=0 \\ \end{align*}

Let \(Y = y -y_{0}\) and \(X = x -x_{0}\) then the above is transformed to new ode in \(Y(X)\)

\[ \frac {d}{d X}Y \left (X \right ) = \frac {-X -x_{0} +2 Y \left (X \right )+2 y_{0} +3}{2 X +2 x_{0} +Y \left (X \right )+y_{0} -1} \]

Solving for possible values of \(x_{0}\) and \(y_{0}\) which makes the above ode a homogeneous ode results in

\begin{align*} x_{0}&=1\\ y_{0}&=-1 \end{align*}

Using these values now it is possible to easily solve for \(Y \left (X \right )\). The above ode now becomes

\begin{align*} \frac {d}{d X}Y \left (X \right ) = \frac {-X +2 Y \left (X \right )}{2 X +Y \left (X \right )} \end{align*}

In canonical form, the ODE is

\begin{align*} Y' &= F(X,Y)\\ &= \frac {-X +2 Y}{2 X +Y}\tag {1} \end{align*}

An ode of the form \(Y' = \frac {M(X,Y)}{N(X,Y)}\) is called homogeneous if the functions \(M(X,Y)\) and \(N(X,Y)\) are both homogeneous functions and of the same order. Recall that a function \(f(X,Y)\) is homogeneous of order \(n\) if

\[ f(t^n X, t^n Y)= t^n f(X,Y) \]

In this case, it can be seen that both \(M=-X +2 Y\) and \(N=2 X +Y\) are both homogeneous and of the same order \(n=1\). Therefore this is a homogeneous ode. Since this ode is homogeneous, it is converted to separable ODE using the substitution \(u=\frac {Y}{X}\), or \(Y=uX\). Hence

\[ \frac { \mathop {\mathrm {d}Y}}{\mathop {\mathrm {d}X}}= \frac { \mathop {\mathrm {d}u}}{\mathop {\mathrm {d}X}}X + u \]

Applying the transformation \(Y=uX\) to the above ODE in (1) gives

\begin{align*} \frac { \mathop {\mathrm {d}u}}{\mathop {\mathrm {d}X}}X + u &= \frac {2 u -1}{u +2}\\ \frac { \mathop {\mathrm {d}u}}{\mathop {\mathrm {d}X}} &= \frac {\frac {2 u \left (X \right )-1}{u \left (X \right )+2}-u \left (X \right )}{X} \end{align*}

Or

\[ \frac {d}{d X}u \left (X \right )-\frac {\frac {2 u \left (X \right )-1}{u \left (X \right )+2}-u \left (X \right )}{X} = 0 \]

Or

\[ \left (\frac {d}{d X}u \left (X \right )\right ) X u \left (X \right )+u \left (X \right )^{2}+2 \left (\frac {d}{d X}u \left (X \right )\right ) X +1 = 0 \]

Or

\[ X \left (u \left (X \right )+2\right ) \left (\frac {d}{d X}u \left (X \right )\right )+u \left (X \right )^{2}+1 = 0 \]

Which is now solved as separable in \(u \left (X \right )\).

The ode

\begin{equation} \frac {d}{d X}u \left (X \right ) = -\frac {u \left (X \right )^{2}+1}{X \left (u \left (X \right )+2\right )} \end{equation}

is separable as it can be written as

\begin{align*} \frac {d}{d X}u \left (X \right )&= -\frac {u \left (X \right )^{2}+1}{X \left (u \left (X \right )+2\right )}\\ &= f(X) g(u) \end{align*}

Where

\begin{align*} f(X) &= -\frac {1}{X}\\ g(u) &= \frac {u^{2}+1}{u +2} \end{align*}

Integrating gives

\begin{align*} \int { \frac {1}{g(u)} \,du} &= \int { f(X) \,dX} \\ \int { \frac {u +2}{u^{2}+1}\,du} &= \int { -\frac {1}{X} \,dX} \\ \end{align*}

\[ \frac {\ln \left (u \left (X \right )^{2}+1\right )}{2}+2 \arctan \left (u \left (X \right )\right )=\ln \left (\frac {1}{X}\right )+c_1 \]

We now need to find the singular solutions, these are found by finding for what values \(g(u)\) is zero, since we had to divide by this above. Solving \(g(u)=0\) or

\[ \frac {u^{2}+1}{u +2}=0 \]

for \(u \left (X \right )\) gives

\begin{align*} u \left (X \right )&=-i\\ u \left (X \right )&=i \end{align*}

Now we go over each such singular solution and check if it verifies the ode itself and any initial conditions given. If it does not then the singular solution will not be used.

Therefore the solutions found are

\begin{align*} \frac {\ln \left (u \left (X \right )^{2}+1\right )}{2}+2 \arctan \left (u \left (X \right )\right ) &= \ln \left (\frac {1}{X}\right )+c_1 \\ u \left (X \right ) &= -i \\ u \left (X \right ) &= i \\ \end{align*}

Converting \(\frac {\ln \left (u \left (X \right )^{2}+1\right )}{2}+2 \arctan \left (u \left (X \right )\right ) = \ln \left (\frac {1}{X}\right )+c_1\) back to \(Y \left (X \right )\) gives

\begin{align*} \frac {\ln \left (\frac {Y \left (X \right )^{2}+X^{2}}{X^{2}}\right )}{2}+2 \arctan \left (\frac {Y \left (X \right )}{X}\right ) = \ln \left (\frac {1}{X}\right )+c_1 \end{align*}

Converting \(u \left (X \right ) = -i\) back to \(Y \left (X \right )\) gives

\begin{align*} Y \left (X \right ) = -i X \end{align*}

Converting \(u \left (X \right ) = i\) back to \(Y \left (X \right )\) gives

\begin{align*} Y \left (X \right ) = i X \end{align*}

Using the solution for \(Y(X)\)

\begin{align*} \frac {\ln \left (\frac {Y \left (X \right )^{2}+X^{2}}{X^{2}}\right )}{2}+2 \arctan \left (\frac {Y \left (X \right )}{X}\right ) = \ln \left (\frac {1}{X}\right )+c_1\tag {A} \end{align*}

And replacing back terms in the above solution using

\begin{align*} Y &= y +y_{0}\\ X &= x_{0} +x \end{align*}

Or

\begin{align*} Y &= y -1\\ X &= 1+x \end{align*}

Then the solution in \(y\) becomes using EQ (A)

\begin{align*} \frac {\ln \left (\frac {\left (y+1\right )^{2}+\left (x -1\right )^{2}}{\left (x -1\right )^{2}}\right )}{2}+2 \arctan \left (\frac {y+1}{x -1}\right ) = \ln \left (\frac {1}{x -1}\right )+c_1 \end{align*}

Using the solution for \(Y(X)\)

\begin{align*} Y \left (X \right ) = -i X\tag {A} \end{align*}

And replacing back terms in the above solution using

\begin{align*} Y &= y +y_{0}\\ X &= x_{0} +x \end{align*}

Or

\begin{align*} Y &= y -1\\ X &= 1+x \end{align*}

Then the solution in \(y\) becomes using EQ (A)

\begin{align*} y+1 = -i \left (x -1\right ) \end{align*}

Using the solution for \(Y(X)\)

\begin{align*} Y \left (X \right ) = i X\tag {A} \end{align*}

And replacing back terms in the above solution using

\begin{align*} Y &= y +y_{0}\\ X &= x_{0} +x \end{align*}

Or

\begin{align*} Y &= y -1\\ X &= 1+x \end{align*}

Then the solution in \(y\) becomes using EQ (A)

\begin{align*} y+1 = i \left (x -1\right ) \end{align*}

Simplifying the above gives

\begin{align*} \frac {\ln \left (\frac {\left (y+1\right )^{2}+\left (x -1\right )^{2}}{\left (x -1\right )^{2}}\right )}{2}+2 \arctan \left (\frac {y+1}{x -1}\right ) &= \ln \left (\frac {1}{x -1}\right )+c_1 \\ y+1 &= -i x +i \\ y+1 &= i \left (x -1\right ) \\ \end{align*}

Solving for \(y\) gives

\begin{align*} \frac {\ln \left (\frac {\left (y+1\right )^{2}+\left (x -1\right )^{2}}{\left (x -1\right )^{2}}\right )}{2}+2 \arctan \left (\frac {y+1}{x -1}\right ) &= \ln \left (\frac {1}{x -1}\right )+c_1 \\ y &= i x -i-1 \\ y &= -i x +i-1 \\ \end{align*}

Figure 2.22: Slope field \(x -2 y-3+\left (2 x +y-1\right ) y^{\prime } = 0\)

Summary of solutions found

\begin{align*} \frac {\ln \left (\frac {\left (y+1\right )^{2}+\left (x -1\right )^{2}}{\left (x -1\right )^{2}}\right )}{2}+2 \arctan \left (\frac {y+1}{x -1}\right ) &= \ln \left (\frac {1}{x -1}\right )+c_1 \\ y &= i x -i-1 \\ y &= -i x +i-1 \\ \end{align*}

Solve

\begin{align*} x -2 y-3+\left (2 x +y-1\right ) y^{\prime }&=0 \\ \end{align*}

Applying transformation

\begin{align*} y&=\frac {1}{u(x)}-g \end{align*}

Results in the new ode which is Abel first kind

\begin{align*} x -2 x u \left (x \right )-3+\left (2 x +x u \left (x \right )-1\right ) \left (u \left (x \right )+x u^{\prime }\left (x \right )\right ) = 0 \end{align*}

Which is now solved Unknown ode type.

Solved using first_order_ode_abel_second_kind_solved_by_converting_to_first_kind

Time used: 5.990 (sec)

This is Abel second kind ODE, it has the form

\[ \left (y \left (x \right )+g\right )y^{\prime }\left (x \right )= f_0(x)+f_1(x) y \left (x \right ) +f_2(x)y \left (x \right )^{2}+f_3(x)y \left (x \right )^{3} \]

Comparing the above to given ODE which is

\begin{align*}x -2 y \left (x \right )-3+\left (2 x +y \left (x \right )-1\right ) y^{\prime }\left (x \right ) = 0\tag {1} \end{align*}

Shows that

\begin{align*} g &= 2 x -1\\ f_0 &= 3-x\\ f_1 &= 2\\ f_2 &= 0\\ f_3 &= 0 \end{align*}

Applying transformation

\begin{align*} y \left (x \right )&=\frac {1}{u(x)}-g \end{align*}

Results in the new ode which is Abel first kind

\begin{align*} u^{\prime }\left (x \right ) = \left (5 x -5\right ) u \left (x \right )^{3}-4 u \left (x \right )^{2} \end{align*}

Which is now solved.

Solve This is Abel first kind ODE, it has the form

\[ u^{\prime }\left (x \right )= f_0(x)+f_1(x) u \left (x \right ) +f_2(x)u \left (x \right )^{2}+f_3(x)u \left (x \right )^{3} \]

Comparing the above to given ODE which is

\begin{align*}u^{\prime }\left (x \right )&=\left (5 x -5\right ) u \left (x \right )^{3}-4 u \left (x \right )^{2}\tag {1} \end{align*}

Therefore

\begin{align*} f_0 &= 0\\ f_1 &= 0\\ f_2 &= -4\\ f_3 &= 5 x -5 \end{align*}

Hence

\begin{align*} f'_{0} &= 0\\ f'_{3} &= 5 \end{align*}

Since \(f_2(x)=-4\) is not zero, then the followingtransformation is used to remove \(f_2\). Let \(u \left (x \right ) = u(x) - \frac {f_2}{3 f_3}\) or

\begin{align*} u \left (x \right ) &= u(x) - \left ( \frac {-4}{15 x -15} \right ) \\ &= u \left (x \right )+\frac {4}{15 x -15} \end{align*}

The above transformation applied to (1) gives a new ODE as

\begin{align*} u^{\prime }\left (x \right ) = \frac {\left (3375 x^{3}-10125 x^{2}+10125 x -3375\right ) u \left (x \right )^{3}}{675 \left (x -1\right )^{2}}+\frac {\left (-720 x +720\right ) u \left (x \right )}{675 \left (x -1\right )^{2}}+\frac {52}{675 \left (x -1\right )^{2}}\tag {2} \end{align*}

The above ODE (2) can now be solved.

Solve Writing the ode as

\begin{align*} u^{\prime }\left (x \right )&=\frac {3375 u^{3} x^{3}-10125 u^{3} x^{2}+10125 u^{3} x -3375 u^{3}-720 u x +720 u +52}{675 \left (x -1\right )^{2}}\\ u^{\prime }\left (x \right )&= \omega \left ( x,u \left (x \right )\right ) \end{align*}

The condition of Lie symmetry is the linearized PDE given by

\begin{align*} \eta _{x}+\omega \left ( \eta _{u \left (x \right )}-\xi _{x}\right ) -\omega ^{2}\xi _{u \left (x \right )}-\omega _{x}\xi -\omega _{u \left (x \right )}\eta =0\tag {A} \end{align*}

To determine \(\xi ,\eta \) then (A) is solved using ansatz. Making bivariate polynomials of degree 1 to use as anstaz gives

\begin{align*} \tag{1E} \xi &= u a_{3}+x a_{2}+a_{1} \\ \tag{2E} \eta &= u b_{3}+x b_{2}+b_{1} \\ \end{align*}

Where the unknown coefficients are

\[ \{a_{1}, a_{2}, a_{3}, b_{1}, b_{2}, b_{3}\} \]

Substituting equations (1E,2E) and \(\omega \) into (A) gives

\begin{equation} \tag{5E} b_{2}+\frac {\left (3375 u^{3} x^{3}-10125 u^{3} x^{2}+10125 u^{3} x -3375 u^{3}-720 u x +720 u +52\right ) \left (b_{3}-a_{2}\right )}{675 \left (x -1\right )^{2}}-\frac {\left (3375 u^{3} x^{3}-10125 u^{3} x^{2}+10125 u^{3} x -3375 u^{3}-720 u x +720 u +52\right )^{2} a_{3}}{455625 \left (x -1\right )^{4}}-\left (\frac {10125 u^{3} x^{2}-20250 u^{3} x +10125 u^{3}-720 u}{675 \left (x -1\right )^{2}}-\frac {2 \left (3375 u^{3} x^{3}-10125 u^{3} x^{2}+10125 u^{3} x -3375 u^{3}-720 u x +720 u +52\right )}{675 \left (x -1\right )^{3}}\right ) \left (u a_{3}+x a_{2}+a_{1}\right )-\frac {\left (10125 u^{2} x^{3}-30375 u^{2} x^{2}+30375 u^{2} x -10125 u^{2}-720 x +720\right ) \left (u b_{3}+x b_{2}+b_{1}\right )}{675 \left (x -1\right )^{2}} = 0 \end{equation}

Putting the above in normal form gives

\[ -\frac {11390625 u^{6} x^{6} a_{3}-68343750 u^{6} x^{5} a_{3}[phone] u^{6} x^{4} a_{3}-227812500 u^{6} x^{3} a_{3}[phone] u^{6} x^{2} a_{3}-2581875 u^{4} x^{4} a_{3}+4556250 u^{3} x^{5} a_{2}+4556250 u^{3} x^{5} b_{3}+6834375 u^{2} x^{6} b_{2}-68343750 u^{6} x a_{3}[phone] u^{4} x^{3} a_{3}+2278125 u^{3} x^{4} a_{1}-20503125 u^{3} x^{4} a_{2}-22781250 u^{3} x^{4} b_{3}+6834375 u^{2} x^{5} b_{1}-34171875 u^{2} x^{5} b_{2}[phone] u^{6} a_{3}-15491250 u^{4} x^{2} a_{3}-9112500 u^{3} x^{3} a_{1}[phone] u^{3} x^{3} a_{2}+351000 u^{3} x^{3} a_{3}[phone] u^{3} x^{3} b_{3}-34171875 u^{2} x^{4} b_{1}[phone] u^{2} x^{4} b_{2}[phone] u^{4} x a_{3}[phone] u^{3} x^{2} a_{1}-31893750 u^{3} x^{2} a_{2}-1053000 u^{3} x^{2} a_{3}-45562500 u^{3} x^{2} b_{3}[phone] u^{2} x^{3} b_{1}-68343750 u^{2} x^{3} b_{2}-2581875 u^{4} a_{3}-9112500 u^{3} x a_{1}[phone] u^{3} x a_{2}+1053000 u^{3} x a_{3}[phone] u^{3} x b_{3}+1004400 u^{2} x^{2} a_{3}-68343750 u^{2} x^{2} b_{1}[phone] u^{2} x^{2} b_{2}-941625 x^{4} b_{2}+2278125 u^{3} a_{1}-2278125 u^{3} a_{2}-351000 u^{3} a_{3}-4556250 u^{3} b_{3}-2008800 u^{2} x a_{3}[phone] u^{2} x b_{1}-6834375 u^{2} x b_{2}+486000 u \,x^{2} a_{1}+486000 u \,x^{2} a_{2}-486000 x^{3} b_{1}+3280500 x^{3} b_{2}+1004400 u^{2} a_{3}-6834375 u^{2} b_{1}-972000 u x a_{1}-972000 u x a_{2}-145080 u x a_{3}-35100 x^{2} a_{2}+1458000 x^{2} b_{1}-4191750 x^{2} b_{2}-35100 x^{2} b_{3}+486000 u a_{1}+486000 u a_{2}+145080 u a_{3}-70200 x a_{1}-1458000 x b_{1}+2308500 x b_{2}+70200 x b_{3}+70200 a_{1}+35100 a_{2}+2704 a_{3}+486000 b_{1}-455625 b_{2}-35100 b_{3}}{455625 \left (x -1\right )^{4}} = 0 \]

Setting the numerator to zero gives

\begin{equation} \tag{6E} -11390625 u^{6} x^{6} a_{3}[phone] u^{6} x^{5} a_{3}-170859375 u^{6} x^{4} a_{3}[phone] u^{6} x^{3} a_{3}-170859375 u^{6} x^{2} a_{3}+2581875 u^{4} x^{4} a_{3}-4556250 u^{3} x^{5} a_{2}-4556250 u^{3} x^{5} b_{3}-6834375 u^{2} x^{6} b_{2}[phone] u^{6} x a_{3}-10327500 u^{4} x^{3} a_{3}-2278125 u^{3} x^{4} a_{1}[phone] u^{3} x^{4} a_{2}[phone] u^{3} x^{4} b_{3}-6834375 u^{2} x^{5} b_{1}[phone] u^{2} x^{5} b_{2}-11390625 u^{6} a_{3}[phone] u^{4} x^{2} a_{3}+9112500 u^{3} x^{3} a_{1}-36450000 u^{3} x^{3} a_{2}-351000 u^{3} x^{3} a_{3}-45562500 u^{3} x^{3} b_{3}[phone] u^{2} x^{4} b_{1}-68343750 u^{2} x^{4} b_{2}-10327500 u^{4} x a_{3}-13668750 u^{3} x^{2} a_{1}[phone] u^{3} x^{2} a_{2}+1053000 u^{3} x^{2} a_{3}[phone] u^{3} x^{2} b_{3}-68343750 u^{2} x^{3} b_{1}[phone] u^{2} x^{3} b_{2}+2581875 u^{4} a_{3}+9112500 u^{3} x a_{1}-13668750 u^{3} x a_{2}-1053000 u^{3} x a_{3}-22781250 u^{3} x b_{3}-1004400 u^{2} x^{2} a_{3}[phone] u^{2} x^{2} b_{1}-34171875 u^{2} x^{2} b_{2}+941625 x^{4} b_{2}-2278125 u^{3} a_{1}+2278125 u^{3} a_{2}+351000 u^{3} a_{3}+4556250 u^{3} b_{3}+2008800 u^{2} x a_{3}-34171875 u^{2} x b_{1}+6834375 u^{2} x b_{2}-486000 u \,x^{2} a_{1}-486000 u \,x^{2} a_{2}+486000 x^{3} b_{1}-3280500 x^{3} b_{2}-1004400 u^{2} a_{3}+6834375 u^{2} b_{1}+972000 u x a_{1}+972000 u x a_{2}+145080 u x a_{3}+35100 x^{2} a_{2}-1458000 x^{2} b_{1}+4191750 x^{2} b_{2}+35100 x^{2} b_{3}-486000 u a_{1}-486000 u a_{2}-145080 u a_{3}+70200 x a_{1}+1458000 x b_{1}-2308500 x b_{2}-70200 x b_{3}-70200 a_{1}-35100 a_{2}-2704 a_{3}-486000 b_{1}+455625 b_{2}+35100 b_{3} = 0 \end{equation}

Looking at the above PDE shows the following are all the terms with \(\{u, x\}\) in them.

\[ \{u, x\} \]

The following substitution is now made to be able to collect on all terms with \(\{u, x\}\) in them

\[ \{u = v_{1}, x = v_{2}\} \]

The above PDE (6E) now becomes

\begin{equation} \tag{7E} -11390625 a_{3} v_{1}^{6} v_{2}^{6}[phone] a_{3} v_{1}^{6} v_{2}^{5}-170859375 a_{3} v_{1}^{6} v_{2}^{4}[phone] a_{3} v_{1}^{6} v_{2}^{3}-4556250 a_{2} v_{1}^{3} v_{2}^{5}-170859375 a_{3} v_{1}^{6} v_{2}^{2}+2581875 a_{3} v_{1}^{4} v_{2}^{4}-6834375 b_{2} v_{1}^{2} v_{2}^{6}-4556250 b_{3} v_{1}^{3} v_{2}^{5}-2278125 a_{1} v_{1}^{3} v_{2}^{4}[phone] a_{2} v_{1}^{3} v_{2}^{4}[phone] a_{3} v_{1}^{6} v_{2}-10327500 a_{3} v_{1}^{4} v_{2}^{3}-6834375 b_{1} v_{1}^{2} v_{2}^{5}[phone] b_{2} v_{1}^{2} v_{2}^{5}[phone] b_{3} v_{1}^{3} v_{2}^{4}+9112500 a_{1} v_{1}^{3} v_{2}^{3}-36450000 a_{2} v_{1}^{3} v_{2}^{3}-11390625 a_{3} v_{1}^{6}[phone] a_{3} v_{1}^{4} v_{2}^{2}-351000 a_{3} v_{1}^{3} v_{2}^{3}[phone] b_{1} v_{1}^{2} v_{2}^{4}-68343750 b_{2} v_{1}^{2} v_{2}^{4}-45562500 b_{3} v_{1}^{3} v_{2}^{3}-13668750 a_{1} v_{1}^{3} v_{2}^{2}[phone] a_{2} v_{1}^{3} v_{2}^{2}-10327500 a_{3} v_{1}^{4} v_{2}+1053000 a_{3} v_{1}^{3} v_{2}^{2}-68343750 b_{1} v_{1}^{2} v_{2}^{3}[phone] b_{2} v_{1}^{2} v_{2}^{3}[phone] b_{3} v_{1}^{3} v_{2}^{2}+9112500 a_{1} v_{1}^{3} v_{2}-13668750 a_{2} v_{1}^{3} v_{2}+2581875 a_{3} v_{1}^{4}-1053000 a_{3} v_{1}^{3} v_{2}-1004400 a_{3} v_{1}^{2} v_{2}^{2}[phone] b_{1} v_{1}^{2} v_{2}^{2}-34171875 b_{2} v_{1}^{2} v_{2}^{2}+941625 b_{2} v_{2}^{4}-22781250 b_{3} v_{1}^{3} v_{2}-2278125 a_{1} v_{1}^{3}-486000 a_{1} v_{1} v_{2}^{2}+2278125 a_{2} v_{1}^{3}-486000 a_{2} v_{1} v_{2}^{2}+351000 a_{3} v_{1}^{3}+2008800 a_{3} v_{1}^{2} v_{2}-34171875 b_{1} v_{1}^{2} v_{2}+486000 b_{1} v_{2}^{3}+6834375 b_{2} v_{1}^{2} v_{2}-3280500 b_{2} v_{2}^{3}+4556250 b_{3} v_{1}^{3}+972000 a_{1} v_{1} v_{2}+972000 a_{2} v_{1} v_{2}+35100 a_{2} v_{2}^{2}-1004400 a_{3} v_{1}^{2}+145080 a_{3} v_{1} v_{2}+6834375 b_{1} v_{1}^{2}-1458000 b_{1} v_{2}^{2}+4191750 b_{2} v_{2}^{2}+35100 b_{3} v_{2}^{2}-486000 a_{1} v_{1}+70200 a_{1} v_{2}-486000 a_{2} v_{1}-145080 a_{3} v_{1}+1458000 b_{1} v_{2}-2308500 b_{2} v_{2}-70200 b_{3} v_{2}-70200 a_{1}-35100 a_{2}-2704 a_{3}-486000 b_{1}+455625 b_{2}+35100 b_{3} = 0 \end{equation}

Collecting the above on the terms \(v_i\) introduced, and these are

\[ \{v_{1}, v_{2}\} \]

Equation (7E) now becomes

\begin{equation} \tag{8E} \left (-4556250 a_{2}-4556250 b_{3}\right ) v_{1}^{3} v_{2}^{5}+\left (-2278125 a_{1}[phone] a_{2}[phone] b_{3}\right ) v_{1}^{3} v_{2}^{4}+\left (9112500 a_{1}-36450000 a_{2}-351000 a_{3}-45562500 b_{3}\right ) v_{1}^{3} v_{2}^{3}+\left (-13668750 a_{1}[phone] a_{2}+1053000 a_{3}[phone] b_{3}\right ) v_{1}^{3} v_{2}^{2}+\left (9112500 a_{1}-13668750 a_{2}-1053000 a_{3}-22781250 b_{3}\right ) v_{1}^{3} v_{2}+\left (-6834375 b_{1}[phone] b_{2}\right ) v_{1}^{2} v_{2}^{5}+\left (34171875 b_{1}-68343750 b_{2}\right ) v_{1}^{2} v_{2}^{4}+\left (-68343750 b_{1}[phone] b_{2}\right ) v_{1}^{2} v_{2}^{3}+\left (-1004400 a_{3}[phone] b_{1}-34171875 b_{2}\right ) v_{1}^{2} v_{2}^{2}+\left (2008800 a_{3}-34171875 b_{1}+6834375 b_{2}\right ) v_{1}^{2} v_{2}+\left (-486000 a_{1}-486000 a_{2}\right ) v_{1} v_{2}^{2}+\left (972000 a_{1}+972000 a_{2}+145080 a_{3}\right ) v_{1} v_{2}+\left (-2278125 a_{1}+2278125 a_{2}+351000 a_{3}+4556250 b_{3}\right ) v_{1}^{3}-11390625 a_{3} v_{1}^{6} v_{2}^{6}[phone] a_{3} v_{1}^{6} v_{2}^{5}-170859375 a_{3} v_{1}^{6} v_{2}^{4}[phone] a_{3} v_{1}^{6} v_{2}^{3}-11390625 a_{3} v_{1}^{6}+2581875 a_{3} v_{1}^{4}+941625 b_{2} v_{2}^{4}-70200 a_{1}-35100 a_{2}-2704 a_{3}-486000 b_{1}+455625 b_{2}+35100 b_{3}+\left (-1004400 a_{3}+6834375 b_{1}\right ) v_{1}^{2}+\left (-486000 a_{1}-486000 a_{2}-145080 a_{3}\right ) v_{1}+\left (486000 b_{1}-3280500 b_{2}\right ) v_{2}^{3}+\left (35100 a_{2}-1458000 b_{1}+4191750 b_{2}+35100 b_{3}\right ) v_{2}^{2}+\left (70200 a_{1}+1458000 b_{1}-2308500 b_{2}-70200 b_{3}\right ) v_{2}-170859375 a_{3} v_{1}^{6} v_{2}^{2}+2581875 a_{3} v_{1}^{4} v_{2}^{4}-6834375 b_{2} v_{1}^{2} v_{2}^{6}[phone] a_{3} v_{1}^{6} v_{2}-10327500 a_{3} v_{1}^{4} v_{2}^{3}[phone] a_{3} v_{1}^{4} v_{2}^{2}-10327500 a_{3} v_{1}^{4} v_{2} = 0 \end{equation}

Setting each coefficients in (8E) to zero gives the following equations to solve

\begin{align*} -170859375 a_{3}&=0\\ -11390625 a_{3}&=0\\ -10327500 a_{3}&=0\\ 2581875 a_{3}&=0\\ 15491250 a_{3}&=0\\ 68343750 a_{3}&=0\\ 227812500 a_{3}&=0\\ -6834375 b_{2}&=0\\ 941625 b_{2}&=0\\ -486000 a_{1}-486000 a_{2}&=0\\ -4556250 a_{2}-4556250 b_{3}&=0\\ -1004400 a_{3}+6834375 b_{1}&=0\\ -68343750 b_{1}[phone] b_{2}&=0\\ -6834375 b_{1}[phone] b_{2}&=0\\ 486000 b_{1}-3280500 b_{2}&=0\\ 34171875 b_{1}-68343750 b_{2}&=0\\ -2278125 a_{1}[phone] a_{2}[phone] b_{3}&=0\\ -486000 a_{1}-486000 a_{2}-145080 a_{3}&=0\\ 972000 a_{1}+972000 a_{2}+145080 a_{3}&=0\\ -1004400 a_{3}[phone] b_{1}-34171875 b_{2}&=0\\ 2008800 a_{3}-34171875 b_{1}+6834375 b_{2}&=0\\ -13668750 a_{1}[phone] a_{2}+1053000 a_{3}[phone] b_{3}&=0\\ -2278125 a_{1}+2278125 a_{2}+351000 a_{3}+4556250 b_{3}&=0\\ 70200 a_{1}+1458000 b_{1}-2308500 b_{2}-70200 b_{3}&=0\\ 9112500 a_{1}-36450000 a_{2}-351000 a_{3}-45562500 b_{3}&=0\\ 9112500 a_{1}-13668750 a_{2}-1053000 a_{3}-22781250 b_{3}&=0\\ 35100 a_{2}-1458000 b_{1}+4191750 b_{2}+35100 b_{3}&=0\\ -70200 a_{1}-35100 a_{2}-2704 a_{3}-486000 b_{1}+455625 b_{2}+35100 b_{3}&=0 \end{align*}

Solving the above equations for the unknowns gives

\begin{align*} a_{1}&=b_{3}\\ a_{2}&=-b_{3}\\ a_{3}&=0\\ b_{1}&=0\\ b_{2}&=0\\ b_{3}&=b_{3} \end{align*}

Substituting the above solution in the anstaz (1E,2E) (using \(1\) as arbitrary value for any unknown in the RHS) gives

\begin{align*} \xi &= 1-x \\ \eta &= u \\ \end{align*}

Shifting is now applied to make \(\xi =0\) in order to simplify the rest of the computation

\begin{align*} \eta &= \eta - \omega \left (x,u\right ) \xi \\ &= u - \left (\frac {3375 u^{3} x^{3}-10125 u^{3} x^{2}+10125 u^{3} x -3375 u^{3}-720 u x +720 u +52}{675 \left (x -1\right )^{2}}\right ) \left (1-x\right ) \\ &= \frac {52+3375 \left (x -1\right )^{3} u^{3}+\left (-45 x +45\right ) u}{675 x -675}\\ \xi &= 0 \end{align*}

The next step is to determine the canonical coordinates \(R,S\). The canonical coordinates map \(\left ( x,u\right ) \to \left ( R,S \right )\) where \(\left ( R,S \right )\) are the canonical coordinates which make the original ode become a quadrature and hence solved by integration.

The characteristic pde which is used to find the canonical coordinates is

\begin{align*} \frac {d x}{\xi } &= \frac {d u}{\eta } = dS \tag {1} \end{align*}

The above comes from the requirements that \(\left ( \xi \frac {\partial }{\partial x} + \eta \frac {\partial }{\partial u}\right ) S(x,u) = 1\). Starting with the first pair of ode’s in (1) gives an ode to solve for the independent variable \(R\) in the canonical coordinates, where \(S(R)\). Since \(\xi =0\) then in this special case

\begin{align*} R = x \end{align*}

\(S\) is found from

\begin{align*} S &= \int { \frac {1}{\eta }} dy\\ &= \int { \frac {1}{\frac {52+3375 \left (x -1\right )^{3} u^{3}+\left (-45 x +45\right ) u}{675 x -675}}} dy \end{align*}

Which results in

\begin{align*} S&= \left (675 x -675\right ) \left (\frac {\left (-15 x +15\right ) \ln \left (225 u^{2} x^{2}-450 u^{2} x +225 u^{2}-60 u x +60 u +13\right )}{20250 x^{2}-40500 x +20250}+\frac {2 \left (8-\frac {\left (-15 x +15\right ) \left (-60 x +60\right )}{2 \left (225 x^{2}-450 x +225\right )}\right ) \arctan \left (\frac {2 \left (225 x^{2}-450 x +225\right ) u -60 x +60}{90 x -90}\right )}{45 \left (90 x -90\right )}+\frac {\ln \left (15 u x -15 u +4\right )}{675 x -675}\right ) \end{align*}

Now that \(R,S\) are found, we need to setup the ode in these coordinates. This is done by evaluating

\begin{align*} \frac {dS}{dR} &= \frac { S_{x} + \omega (x,u) S_{u} }{ R_{x} + \omega (x,u) R_{u} }\tag {2} \end{align*}

Where in the above \(R_{x},R_{u},S_{x},S_{u}\) are all partial derivatives and \(\omega (x,u)\) is the right hand side of the original ode given by

\begin{align*} \omega (x,u) &= \frac {3375 u^{3} x^{3}-10125 u^{3} x^{2}+10125 u^{3} x -3375 u^{3}-720 u x +720 u +52}{675 \left (x -1\right )^{2}} \end{align*}

Evaluating all the partial derivatives gives

\begin{align*} R_{x} &= 1\\ R_{u} &= 0\\ S_{x} &= \frac {u}{5 \left (\frac {4}{15}+\left (x -1\right ) u \right ) \left (\frac {13}{225}+\left (x -1\right )^{2} u^{2}+\frac {4 \left (1-x \right ) u}{15}\right )}\\ S_{u} &= \frac {x -1}{5 \left (\frac {4}{15}+\left (x -1\right ) u \right ) \left (\frac {13}{225}+\left (x -1\right )^{2} u^{2}+\frac {4 \left (1-x \right ) u}{15}\right )} \end{align*}

Substituting all the above in (2) and simplifying gives the ode in canonical coordinates.

\begin{align*} \frac {dS}{dR} &= \frac {1}{x -1}\tag {2A} \end{align*}

We now need to express the RHS as function of \(R\) only. This is done by solving for \(x,u\) in terms of \(R,S\) from the result obtained earlier and simplifying. This gives

\begin{align*} \frac {dS}{dR} &= \frac {1}{R -1} \end{align*}

The above is a quadrature ode. This is the whole point of Lie symmetry method. It converts an ode, no matter how complicated it is, to one that can be solved by integration when the ode is in the canonical coordiates \(R,S\).

Since the ode has the form \(\frac {d}{d R}S \left (R \right )=f(R)\), then we only need to integrate \(f(R)\).

\begin{align*} \int {dS} &= \int {\frac {1}{R -1}\, dR}\\ S \left (R \right ) &= \ln \left (R -1\right ) + c_2 \end{align*}

To complete the solution, we just need to transform the above back to \(x,u\) coordinates. This results in

\begin{align*} 2 \arctan \left (-\frac {2}{3}+5 \left (x -1\right ) u \left (x \right )\right )-\frac {\ln \left (13+225 \left (x -1\right )^{2} u \left (x \right )^{2}+\left (-60 x +60\right ) u \left (x \right )\right )}{2}+\ln \left (4+15 \left (x -1\right ) u \left (x \right )\right ) = \ln \left (x -1\right )+c_2 \end{align*}

Substituting \(u=u \left (x \right )-\frac {4}{3 \left (5 x -5\right )}\) in the above solution gives

\begin{align*} -2 \arctan \left (\frac {2}{3}-5 \left (x -1\right ) \left (u \left (x \right )-\frac {4}{3 \left (5 x -5\right )}\right )\right )-\frac {\ln \left (13+225 \left (x -1\right )^{2} \left (u \left (x \right )-\frac {4}{3 \left (5 x -5\right )}\right )^{2}+\left (-60 x +60\right ) \left (u \left (x \right )-\frac {4}{3 \left (5 x -5\right )}\right )\right )}{2}+\ln \left (4+15 \left (x -1\right ) \left (u \left (x \right )-\frac {4}{3 \left (5 x -5\right )}\right )\right ) = \ln \left (x -1\right )+c_2 \end{align*}

Simplifying the above gives

\begin{align*} 2 \arctan \left (-2+\left (5 x -5\right ) u \left (x \right )\right )+\frac {\ln \left (5\right )}{2}-\frac {\ln \left (1+5 \left (x -1\right )^{2} u \left (x \right )^{2}+\left (-4 x +4\right ) u \left (x \right )\right )}{2}+\ln \left (u \left (x \right ) \left (x -1\right )\right ) &= \ln \left (x -1\right )+c_2 \\ \end{align*}

Substituting \(u \left (x \right )=\frac {1}{2 x +y \left (x \right )-1}\) in the above solution gives

\[ 2 \arctan \left (-2+\frac {5 x -5}{2 x +y \left (x \right )-1}\right )+\frac {\ln \left (5\right )}{2}-\frac {\ln \left (1+\frac {5 \left (x -1\right )^{2}}{\left (2 x +y \left (x \right )-1\right )^{2}}+\frac {-4 x +4}{2 x +y \left (x \right )-1}\right )}{2}+\ln \left (\frac {x -1}{2 x +y \left (x \right )-1}\right ) = \ln \left (x -1\right )+c_2 \]

Simplifying the above gives

\begin{align*} 2 \arctan \left (\frac {x -2 y \left (x \right )-3}{2 x +y \left (x \right )-1}\right )+\frac {\ln \left (5\right )}{2}-\frac {\ln \left (\frac {y \left (x \right )^{2}+x^{2}+2 y \left (x \right )-2 x +2}{\left (2 x +y \left (x \right )-1\right )^{2}}\right )}{2}+\ln \left (\frac {x -1}{2 x +y \left (x \right )-1}\right ) &= \ln \left (x -1\right )+c_2 \\ \end{align*}

Figure 2.23: Slope field \(x -2 y \left (x \right )-3+\left (2 x +y \left (x \right )-1\right ) y^{\prime }\left (x \right ) = 0\)

Figure 2.24: Slope field \(x -2 y \left (x \right )-3+\left (2 x +y \left (x \right )-1\right ) y^{\prime }\left (x \right ) = 0\)

Summary of solutions found

\begin{align*} 2 \arctan \left (\frac {x -2 y \left (x \right )-3}{2 x +y \left (x \right )-1}\right )+\frac {\ln \left (5\right )}{2}-\frac {\ln \left (\frac {y \left (x \right )^{2}+x^{2}+2 y \left (x \right )-2 x +2}{\left (2 x +y \left (x \right )-1\right )^{2}}\right )}{2}+\ln \left (\frac {x -1}{2 x +y \left (x \right )-1}\right ) &= \ln \left (x -1\right )+c_2 \\ \end{align*}

Solved using first_order_ode_LIE

Time used: 0.807 (sec)

Solve

\begin{align*} x -2 y \left (x \right )-3+\left (2 x +y \left (x \right )-1\right ) y^{\prime }\left (x \right )&=0 \\ \end{align*}

Writing the ode as

\begin{align*} y^{\prime }\left (x \right )&=\frac {-x +2 y +3}{2 x +y -1}\\ y^{\prime }\left (x \right )&= \omega \left ( x,y \left (x \right )\right ) \end{align*}

The condition of Lie symmetry is the linearized PDE given by

\begin{align*} \eta _{x}+\omega \left ( \eta _{y \left (x \right )}-\xi _{x}\right ) -\omega ^{2}\xi _{y \left (x \right )}-\omega _{x}\xi -\omega _{y \left (x \right )}\eta =0\tag {A} \end{align*}

To determine \(\xi ,\eta \) then (A) is solved using ansatz. Making bivariate polynomials of degree 1 to use as anstaz gives

\begin{align*} \tag{1E} \xi &= x a_{2}+y a_{3}+a_{1} \\ \tag{2E} \eta &= x b_{2}+y b_{3}+b_{1} \\ \end{align*}

Where the unknown coefficients are

\[ \{a_{1}, a_{2}, a_{3}, b_{1}, b_{2}, b_{3}\} \]

Substituting equations (1E,2E) and \(\omega \) into (A) gives

\begin{equation} \tag{5E} b_{2}+\frac {\left (-x +2 y +3\right ) \left (b_{3}-a_{2}\right )}{2 x +y -1}-\frac {\left (-x +2 y +3\right )^{2} a_{3}}{\left (2 x +y -1\right )^{2}}-\left (-\frac {1}{2 x +y -1}-\frac {2 \left (-x +2 y +3\right )}{\left (2 x +y -1\right )^{2}}\right ) \left (x a_{2}+y a_{3}+a_{1}\right )-\left (\frac {2}{2 x +y -1}-\frac {-x +2 y +3}{\left (2 x +y -1\right )^{2}}\right ) \left (x b_{2}+y b_{3}+b_{1}\right ) = 0 \end{equation}

Putting the above in normal form gives

\[ \frac {2 x^{2} a_{2}-x^{2} a_{3}-x^{2} b_{2}-2 x^{2} b_{3}+2 x y a_{2}+4 x y a_{3}+4 x y b_{2}-2 x y b_{3}-2 y^{2} a_{2}+y^{2} a_{3}+y^{2} b_{2}+2 y^{2} b_{3}-2 x a_{2}+6 x a_{3}-5 x b_{1}+x b_{2}+7 x b_{3}+5 y a_{1}-y a_{2}-7 y a_{3}-2 y b_{2}+6 y b_{3}+5 a_{1}+3 a_{2}-9 a_{3}+5 b_{1}+b_{2}-3 b_{3}}{\left (2 x +y -1\right )^{2}} = 0 \]

Setting the numerator to zero gives

\begin{equation} \tag{6E} 2 x^{2} a_{2}-x^{2} a_{3}-x^{2} b_{2}-2 x^{2} b_{3}+2 x y a_{2}+4 x y a_{3}+4 x y b_{2}-2 x y b_{3}-2 y^{2} a_{2}+y^{2} a_{3}+y^{2} b_{2}+2 y^{2} b_{3}-2 x a_{2}+6 x a_{3}-5 x b_{1}+x b_{2}+7 x b_{3}+5 y a_{1}-y a_{2}-7 y a_{3}-2 y b_{2}+6 y b_{3}+5 a_{1}+3 a_{2}-9 a_{3}+5 b_{1}+b_{2}-3 b_{3} = 0 \end{equation}

Looking at the above PDE shows the following are all the terms with \(\{x, y\}\) in them.

\[ \{x, y\} \]

The following substitution is now made to be able to collect on all terms with \(\{x, y\}\) in them

\[ \{x = v_{1}, y = v_{2}\} \]

The above PDE (6E) now becomes

\begin{equation} \tag{7E} 2 a_{2} v_{1}^{2}+2 a_{2} v_{1} v_{2}-2 a_{2} v_{2}^{2}-a_{3} v_{1}^{2}+4 a_{3} v_{1} v_{2}+a_{3} v_{2}^{2}-b_{2} v_{1}^{2}+4 b_{2} v_{1} v_{2}+b_{2} v_{2}^{2}-2 b_{3} v_{1}^{2}-2 b_{3} v_{1} v_{2}+2 b_{3} v_{2}^{2}+5 a_{1} v_{2}-2 a_{2} v_{1}-a_{2} v_{2}+6 a_{3} v_{1}-7 a_{3} v_{2}-5 b_{1} v_{1}+b_{2} v_{1}-2 b_{2} v_{2}+7 b_{3} v_{1}+6 b_{3} v_{2}+5 a_{1}+3 a_{2}-9 a_{3}+5 b_{1}+b_{2}-3 b_{3} = 0 \end{equation}

Collecting the above on the terms \(v_i\) introduced, and these are

\[ \{v_{1}, v_{2}\} \]

Equation (7E) now becomes

\begin{equation} \tag{8E} \left (2 a_{2}-a_{3}-b_{2}-2 b_{3}\right ) v_{1}^{2}+\left (2 a_{2}+4 a_{3}+4 b_{2}-2 b_{3}\right ) v_{1} v_{2}+\left (-2 a_{2}+6 a_{3}-5 b_{1}+b_{2}+7 b_{3}\right ) v_{1}+\left (-2 a_{2}+a_{3}+b_{2}+2 b_{3}\right ) v_{2}^{2}+\left (5 a_{1}-a_{2}-7 a_{3}-2 b_{2}+6 b_{3}\right ) v_{2}+5 a_{1}+3 a_{2}-9 a_{3}+5 b_{1}+b_{2}-3 b_{3} = 0 \end{equation}

Setting each coefficients in (8E) to zero gives the following equations to solve

\begin{align*} -2 a_{2}+a_{3}+b_{2}+2 b_{3}&=0\\ 2 a_{2}-a_{3}-b_{2}-2 b_{3}&=0\\ 2 a_{2}+4 a_{3}+4 b_{2}-2 b_{3}&=0\\ 5 a_{1}-a_{2}-7 a_{3}-2 b_{2}+6 b_{3}&=0\\ -2 a_{2}+6 a_{3}-5 b_{1}+b_{2}+7 b_{3}&=0\\ 5 a_{1}+3 a_{2}-9 a_{3}+5 b_{1}+b_{2}-3 b_{3}&=0 \end{align*}

Solving the above equations for the unknowns gives

\begin{align*} a_{1}&=-b_{2}-b_{3}\\ a_{2}&=b_{3}\\ a_{3}&=-b_{2}\\ b_{1}&=-b_{2}+b_{3}\\ b_{2}&=b_{2}\\ b_{3}&=b_{3} \end{align*}

Substituting the above solution in the anstaz (1E,2E) (using \(1\) as arbitrary value for any unknown in the RHS) gives

\begin{align*} \xi &= x -1 \\ \eta &= y +1 \\ \end{align*}

Shifting is now applied to make \(\xi =0\) in order to simplify the rest of the computation

\begin{align*} \eta &= \eta - \omega \left (x,y\right ) \xi \\ &= y +1 - \left (\frac {-x +2 y +3}{2 x +y -1}\right ) \left (x -1\right ) \\ &= \frac {x^{2}+y^{2}-2 x +2 y +2}{2 x +y -1}\\ \xi &= 0 \end{align*}

The next step is to determine the canonical coordinates \(R,S\). The canonical coordinates map \(\left ( x,y\right ) \to \left ( R,S \right )\) where \(\left ( R,S \right )\) are the canonical coordinates which make the original ode become a quadrature and hence solved by integration.

The characteristic pde which is used to find the canonical coordinates is

\begin{align*} \frac {d x}{\xi } &= \frac {d y}{\eta } = dS \tag {1} \end{align*}

The above comes from the requirements that \(\left ( \xi \frac {\partial }{\partial x} + \eta \frac {\partial }{\partial y}\right ) S(x,y) = 1\). Starting with the first pair of ode’s in (1) gives an ode to solve for the independent variable \(R\) in the canonical coordinates, where \(S(R)\). Since \(\xi =0\) then in this special case

\begin{align*} R = x \end{align*}

\(S\) is found from

\begin{align*} S &= \int { \frac {1}{\eta }} dy\\ &= \int { \frac {1}{\frac {x^{2}+y^{2}-2 x +2 y +2}{2 x +y -1}}} dy \end{align*}

Which results in

\begin{align*} S&= \frac {\ln \left (x^{2}+y^{2}-2 x +2 y +2\right )}{2}+2 \arctan \left (\frac {2 y +2}{2 x -2}\right ) \end{align*}

Now that \(R,S\) are found, we need to setup the ode in these coordinates. This is done by evaluating

\begin{align*} \frac {dS}{dR} &= \frac { S_{x} + \omega (x,y) S_{y} }{ R_{x} + \omega (x,y) R_{y} }\tag {2} \end{align*}

Where in the above \(R_{x},R_{y},S_{x},S_{y}\) are all partial derivatives and \(\omega (x,y)\) is the right hand side of the original ode given by

\begin{align*} \omega (x,y) &= \frac {-x +2 y +3}{2 x +y -1} \end{align*}

Evaluating all the partial derivatives gives

\begin{align*} R_{x} &= 1\\ R_{y} &= 0\\ S_{x} &= \frac {x -2 y -3}{x^{2}+y^{2}-2 x +2 y +2}\\ S_{y} &= \frac {2 x +y -1}{x^{2}+y^{2}-2 x +2 y +2} \end{align*}

Substituting all the above in (2) and simplifying gives the ode in canonical coordinates.

\begin{align*} \frac {dS}{dR} &= 0\tag {2A} \end{align*}

We now need to express the RHS as function of \(R\) only. This is done by solving for \(x,y\) in terms of \(R,S\) from the result obtained earlier and simplifying. This gives

\begin{align*} \frac {dS}{dR} &= 0 \end{align*}

The above is a quadrature ode. This is the whole point of Lie symmetry method. It converts an ode, no matter how complicated it is, to one that can be solved by integration when the ode is in the canonical coordiates \(R,S\).

Since the ode has the form \(\frac {d}{d R}S \left (R \right )=f(R)\), then we only need to integrate \(f(R)\).

\begin{align*} \int {dS} &= \int {0\, dR} + c_2 \\ S \left (R \right ) &= c_2 \end{align*}

To complete the solution, we just need to transform the above back to \(x,y\) coordinates. This results in

\begin{align*} \frac {\ln \left (y \left (x \right )^{2}+x^{2}+2 y \left (x \right )-2 x +2\right )}{2}+2 \arctan \left (\frac {y \left (x \right )+1}{x -1}\right ) = c_2 \end{align*}

The following diagram shows solution curves of the original ode and how they transform in the canonical coordinates space using the mapping shown.

Original ode in \(x,y\) coordinates	Canonical coordinates transformation	ODE in canonical coordinates \((R,S)\)
\( \frac {dy}{dx} = \frac {-x +2 y +3}{2 x +y -1}\)		\( \frac {d S}{d R} = 0\)
	\(\!\begin {aligned} R&= x\\ S&= \frac {\ln \left (x^{2}+y^{2}-2 x +2 y +2\right )}{2}+2 \arctan \left (\frac {y +1}{x -1}\right ) \end {aligned} \)

Figure 2.25: Slope field \(x -2 y \left (x \right )-3+\left (2 x +y \left (x \right )-1\right ) y^{\prime }\left (x \right ) = 0\)

Summary of solutions found

\begin{align*} \frac {\ln \left (y \left (x \right )^{2}+x^{2}+2 y \left (x \right )-2 x +2\right )}{2}+2 \arctan \left (\frac {y \left (x \right )+1}{x -1}\right ) &= c_2 \\ \end{align*}

✓ Maple. Time used: 0.017 (sec). Leaf size: 31

ode:=x-2*y(x)-3+(2*x+y(x)-1)*diff(y(x),x) = 0; 
dsolve(ode,y(x), singsol=all);
 

\[ y = -1-\tan \left (\operatorname {RootOf}\left (-4 \textit {\_Z} +\ln \left (\sec \left (\textit {\_Z} \right )^{2}\right )+2 \ln \left (x -1\right )+2 c_1 \right )\right ) \left (x -1\right ) \]

Maple trace

Methods for first order ODEs: 
--- Trying classification methods --- 
trying a quadrature 
trying 1st order linear 
trying Bernoulli 
trying separable 
trying inverse linear 
trying homogeneous types: 
trying homogeneous C 
trying homogeneous types: 
trying homogeneous D 
<- homogeneous successful 
<- homogeneous successful
 

Maple step by step

\[ \begin {array}{lll} & {} & \textrm {Let's solve}\hspace {3pt} \\ {} & {} & x -2 y \left (x \right )-3+\left (2 x +y \left (x \right )-1\right ) \left (\frac {d}{d x}y \left (x \right )\right )=0 \\ \bullet & {} & \textrm {Highest derivative means the order of the ODE is}\hspace {3pt} 1 \\ {} & {} & \frac {d}{d x}y \left (x \right ) \\ \bullet & {} & \textrm {Solve for the highest derivative}\hspace {3pt} \\ {} & {} & \frac {d}{d x}y \left (x \right )=\frac {-x +2 y \left (x \right )+3}{2 x +y \left (x \right )-1} \end {array} \]

✓ Mathematica. Time used: 0.035 (sec). Leaf size: 66

ode=(x-2*y[x]-3)+(2*x+y[x]-1)*D[y[x],x]==0; 
ic={}; 
DSolve[{ode,ic},y[x],x,IncludeSingularSolutions->True]
 

\[ \text {Solve}\left [32 \arctan \left (\frac {2 y(x)-x+3}{y(x)+2 x-1}\right )+8 \log \left (\frac {x^2+y(x)^2+2 y(x)-2 x+2}{5 (x-1)^2}\right )+16 \log (x-1)+5 c_1=0,y(x)\right ] \]

✓ Sympy. Time used: 2.882 (sec). Leaf size: 36

from sympy import * 
x = symbols("x") 
y = Function("y") 
ode = Eq(x + (2*x + y(x) - 1)*Derivative(y(x), x) - 2*y(x) - 3,0) 
ics = {} 
dsolve(ode,func=y(x),ics=ics)
 

\[ \log {\left (x - 1 \right )} = C_{1} - \log {\left (\sqrt {1 + \frac {\left (y{\left (x \right )} + 1\right )^{2}}{\left (x - 1\right )^{2}}} \right )} - 2 \operatorname {atan}{\left (\frac {y{\left (x \right )} + 1}{x - 1} \right )} \]