If `A_(alpha)=[(cosalpha,sinalpha),(-sinalpha,cosalpha)] then (A_(alpha))^2=?`
A. `[(cos^2alpha,sin^2alpha),(-sin^2alpha,cos^2alpha)]`
B. `[(cos2alpha,sin2alpha),(-sin2alpha,cos2alpha)]`
C. `[(2cosalpha,2sinalpha),(-sinalpha,2cosalpha)]`
D. none of these
