I've been trying to solve the following differential equation: 3 x + y ( x )

Jaylene Duarte

Jaylene Duarte

Answered question

2022-05-13

I've been trying to solve the following differential equation:
3 x + y ( x ) 2 + d y ( x ) d x ( x 1 ) = 0
And I found out it's an exact differential equation, since it can be rearranged as ( 3 x + y ( x ) 2 ) d x + ( x 1 ) d y = 0
Assuming that a function U ( x , y ) = U x d x + U y d y = k, (where k constant) exists, I calculated it as:
U ( x , y ) = ( 3 x + y 2 ) d x + ( x 1 ) d y = k
And I got
y ( x ) = 3 x 2 2 ( 2 x 1 ) + 2 x 2 x 1 + k 2 x 1
But Mathematica says the solution is
y ( x ) = 3 x 2 2 ( x 1 ) + 2 x x 1 + k 1 x
So either I assumed something which isn't correct or I made a mistake along the process. Where did I go wrong?

Answer & Explanation

Lea Johnson

Lea Johnson

Beginner2022-05-14Added 13 answers

It can be seen as a linear differential equation:
y + y x 1 = 2 3 x x 1
Using integration factor x-1
y ( 1 x ) = ( 2 3 x ) d x
y ( 1 x ) = 2 x 3 x 2 2 + k
Hope it helps

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