Correct approach to this homogeneous differential equation xy^2(dy)/(dx) = y^3 + xy^2 -x^2y - x^3

goorst9Bi

goorst9Bi

Answered question

2022-11-23

Correct approach to this homogeneous differential equation
I am trying to find the general solution to the following equation, but the integral at the end is very complicated and leads me to believe I may have made a mistake somewhere.
x y 2 d y d x = y 3 + x y 2 x 2 y x 3
Which, by the substitution z = y x , can be rearranged into the equation
x d z d x = 1 1 z 1 z 2
This is a separable equation, which I separated into
1 1 1 z 1 z 2 d z = 1 x d x
The right-hand side is easy to solve, but the left-hand integral is giving me trouble. Assuming I did the steps leading up to it correctly, the integral has me stumped. Even WolframaAlpha is unhelpful. My first thought would be to try a partial fraction, but after a few attempts it does not seem to work.
Am I approaching this differential equation correctly? Is there an error I haven't caught?

Answer & Explanation

Dillan Foley

Dillan Foley

Beginner2022-11-24Added 9 answers

Well, assuming that this is the integral to solve, use that
1 1 1 z 1 z 2 = z 2 z 2 z 1 = 1 + z + 1 z 2 z 1 .
That 1 is good as gone. For the remaining part:
z + 1 z 2 z 1 = 1 2 2 z + 2 z 2 z 1 = 1 2 ( 2 z 1 z 2 z 1 + 3 z 2 z 1 ) ,
and substituition solves the first fraction. For the second, the usual approach using partial fractions will do the trick, but the roots of z 2 z 1 seem ugly. Just don't panic.

Do you have a similar question?

Recalculate according to your conditions!

New Questions in Differential Equations

Ask your question.
Get an expert answer.

Let our experts help you. Answer in as fast as 15 minutes.

Didn't find what you were looking for?