1. Differential equations special substitutions

I'm having some trouble solving this differential equation

Solve $\dfrac{dy}{dx}=(y-x)^2$ using the substitution $u=y-x$

Do I have to find $\dfrac{dy}{du}$?

2. Why would you need that? $\dfrac{du}{dx}\;=\;\dfrac{dy}{dx} - 1$ is good enough, isn't it?

3. So would $\dfrac{du}{dx}=u^2-1$

4. Looks good so far.