# Math Help - Substitution problem

1. ## Substitution problem

Hi, I have to solve

$-(y+x)^2/(1+(y+x)^2)=dy/dx$

using the substitution u=y+x. It isn't necessary to explicitly for y in terms of x.

How do I go about doing this? Do I need to use partials when converting to $du/dx$?

Cheers,
Ben

2. Do I need to use partials...
Nope. Just set u = y + x. Then u' = y' + 1. It follows that u' - 1 = y'. Substitute into your DE, and off you go.