Question

Huge problem here -

For what values of a does the boundary value problem:

y''+ ay =0, y(0)=0, y(pi)=0

have nonzero solutions? Consider a=0, positive a=b^2 and negative a=-b^2.

The part I'm confused about is the positive a being equal to B^2 and negative a = -B^2... they just seem like the same thing to me!