Transforming pde to nicer form?

Question

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?

Answer 1

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