How can I solve this differential equation? : xy^2 dy/dx=y^3−x^3

Topniveauh2

Topniveauh2

Answered question

2022-09-23

How can I solve this differential equation? : x y 2 d y d x = y 3 - x 3

Answer & Explanation

Kaiden Stevens

Kaiden Stevens

Beginner2022-09-24Added 12 answers

We have:
x y 2 d y d x = y 3 - x 3
Which is a First Order Nonlinear Ordinary Differential Equation. Let us attempt a substitution of the form:
y = v x
Differentiating wrt x and applying the product rule, we get:
d y d x = v + x d v d x
Substituting into the initial ODE we get:
x ( v x ) 2 ( v + x d v d x ) = ( v x ) 3 - x 3
Then assuming that v , x 0 this simplifies to:
v 2 ( v + x d v d x ) = v 3 - 1
v + x d v d x = v - 1 v 2
x d v d x = - 1 v 2
And we have reduced the initial ODE to a First Order Separable ODE, so we can collect terms and separate the variables to get:
  v 2   d v =   - 1 x   d x
Both integrals are standard, so we can integrate to get:
1 3 v 3 = - ln x + A
v 3 = 3 A - 3 ln x
v = C - 3 ln x 3      , say
Then, we restore the substitution, to get the General Solution:
y x = C - 3 ln x 3
y = x C - 3 ln x 3

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