#### algsubs problem (12.10.00)

I am a relatively new user of maple. I am trying to solve an equation of the form y=(a*c)/(a+b). I would like to solve for another variable x which is equal to a/(a+b). When I use

algsubs(a/(a+b)=x, y);

I receive an error stating: Error, (in algsubs) cannot compute degree of a pattern in a.

##### Tom Cassleman (18.10.00)

I think algsubs cannot recognize a ”buried” pattern. I tried to rewrite your eqation as:

y:=a/(a+b)*c

and then

algsubs(a/(a+b)=x,y);

But that failed to! I think what happens here is that when you enter your equation, maple stores it as

y=a*c/(a+b) and cannot ﬁnd the unique ”pattern” a/(a+b) in that expression. This seems to be a problem with algsubs. Perhaps someone else can ﬁnd a solution.

##### E. Elbraechter (30.10.00)

Note the expression y=(a*c)/(a+b) cannot be handled by algsubs but the substitution expression a/(a+b)=x has not the appropriate form.

First you can change the substitution expression a/(a+b)=x and then use algsubs or subs:

eq_y :=  y = (a*c)/(a+b);
a/(a+b)=x;
isolate(%, (a+b));
algsubs(%, eq_y, b);
subs(%%, eq_y);

a c
eq_y := y = -----
a + b

a
----- = x
a + b

a + b = a/x

y = c x

y = c x

Second you use powsubs of the student package to substitute a factor:

 student[powsubs](a/(a+b)=x, eq_y);

y = c x