89.20.12 problem 12

Internal problem ID [24768]
Book : A short course in Differential Equations. Earl D. Rainville. Second edition. 1958. Macmillan Publisher, NY. CAT 58-5010
Section : Chapter 10. Nonhomogeneous Equations: Operational methods. Oral Exercises at page 154
Problem number : 12
Date solved : Thursday, October 02, 2025 at 10:47:50 PM
CAS classification : [[_2nd_order, _linear, _nonhomogeneous]]

\begin{align*} y^{\prime \prime }+9 y&=\cos \left (3 x \right ) \end{align*}

✓ Maple. Time used: 0.002 (sec). Leaf size: 27

ode:=diff(diff(y(x),x),x)+9*y(x) = cos(3*x); 
dsolve(ode,y(x), singsol=all);
 

\[ y = \frac {\left (18 c_1 +1\right ) \cos \left (3 x \right )}{18}+\frac {\sin \left (3 x \right ) \left (x +6 c_2 \right )}{6} \]

✓ Mathematica. Time used: 0.037 (sec). Leaf size: 31

ode=D[y[x],{x,2}]+9*y[x]== Cos[3*x]; 
ic={}; 
DSolve[{ode,ic},y[x],x,IncludeSingularSolutions->True]
 

\begin{align*} y(x)&\to \left (\frac {1}{36}+c_1\right ) \cos (3 x)+\frac {1}{6} (x+6 c_2) \sin (3 x) \end{align*}

✓ Sympy. Time used: 0.060 (sec). Leaf size: 19

from sympy import * 
x = symbols("x") 
y = Function("y") 
ode = Eq(9*y(x) - cos(3*x) + Derivative(y(x), (x, 2)),0) 
ics = {} 
dsolve(ode,func=y(x),ics=ics)
 

\[ y{\left (x \right )} = C_{2} \cos {\left (3 x \right )} + \left (C_{1} + \frac {x}{6}\right ) \sin {\left (3 x \right )} \]