Don't really know what to do with this one, any help welcome

If A, B andαare constants, independent of x, and

y= Acosαx + Bsinαx

Evaluate the derivates

y'=dy/dx

y^n=d^2y/dx^2

Determine values of A, B and α such that y satisfies

y^n+y=0 and y(0)=0, y'(0)=1

I've tried to differentiate y

y'=-αAsinαx +αBcosαx

y'=αBcosαx- αAsinαx

y^n=-ααBsinαx +ααAcosαx

y^n=ααAcosαx- ααBsinαx