# I How to find the integrating factor? (1st order ODE)

1. Feb 3, 2017

### hellotheworld

x2 + y + y2dx - x dy = 0

Integrating factor, I(x,y) = -1 / (x2 + y2)

How to find the integrating factor ?

Why I cannot use below method to solve the ode ?

(1/N)(My - Nx) = g(x) , I(x,y)=exp( ∫ g(x) dx) OR
(1/M)(My - Nx) = h(y) , I(x,y)=exp( -∫ h(y) dy)

2. Feb 3, 2017

### haruspex

That equation makes no sense. You cannot mix infinitesimals and non-infinitesimals like that.

3. Feb 5, 2017

### Staff: Mentor

Did you mean $(x^2 + y + y^2)dx - x dy = 0$?