Prove the identity!

Cos (pi/2 - x) = sin X

Use your formulae:cos(A-B) = cosAcosB + sinAsinB

cos(\frac{\pi}{2} -x) = cos(\frac{\pi}{2})cos(x) + sin(\frac{\pi}{2})sin(x)

cos (\frac{\pi}{2}) = 0

sin(\frac{\pi}{2}) = 1

cos(\frac{\pi}{2})cos(x) + sin(\frac{\pi}{2})sin(x) = (0)cos(x) + (1)sin(x)

That's all, it's almost finished. You only have to simplify.

I hope it helped! :)