The variables x and y are related by the differential equation:

$\displaystyle \frac{dy}{dx} = \frac{x^2 - y^2}{xy}$

Use the substitution y=xz, where z is a function of x, to obtain the differential equation:

$\displaystyle x\frac{dz}{dx} = \frac{1-az^2}{z}$

My questions sheet has 2 instead of the a, but I get a=1, which is correct?

Cheers.