Recently I have met such an equation: x d y </mrow>

Anthony Kramer

Anthony Kramer

Answered question

2022-05-20

Recently I have met such an equation:
x d y d x = y + x 2 + y 2 d y d x y x = x 2 + y 2 x
First of all what type it has? I can not refer it to any I am aware of(I am a newbie so it is likely that I'm missing something). Trying to solve it gave no result therefore I googled and youtube revealed that I had to use change of variables y = v ( x ) x. However it looks like a cheating. Why use this particular replacement and is there any way to solve it without it?

Answer & Explanation

antantil0

antantil0

Beginner2022-05-21Added 9 answers

x d y d x = y + x 2 + y 2 x d y d x = y + x 1 + y 2 x 2 d y d x = y x + 1 + y 2 x 2
and let y = z x
d y d x = x d z d x + z x d z d x + z = z + 1 + z 2 x d z d x = 1 + z 2 d z 1 + z 2 = d x x
z = tan t d z = d t cos 2 t d t cos t = ln | x | + C cos t cos 2 t d t = ln | x | + C d sin t 1 sin 2 t = ln | x | + C u = sin t d u 1 u 2 = ln | x | + C 1 2 [ 1 1 u + 1 1 + u ] = ln | x | + C 1 2 ln | u + 1 u 1 | = ln | x | + C 1 2 ln | sin ( arctan y x ) + 1 sin ( arctan y x ) 1 | = ln | x | + C 1 2 ln | y + x 2 + y 2 y x 2 + y 2 | = ln | x | + C

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?