Transforming pde to nicer form? I have a second order differential equation for $u$
$$\frac{d^2u}{dx^2} + \frac{d^2u}{dy^2} + 5u = 0$$
I am looking for a transformation $u(x,y) \rightarrow v(x,y)$ that gives
$$\frac{d^2v}{dx^2} + \frac{d^2v}{dy^2} + v = 0$$
Any ideas?

You can do a transform $x \mapsto \frac{a}{5},y \mapsto \frac{b}{5}$
