Question

verify trig identity and state justifications
sin(x + pi/2) = cosx

Answer 1

sin (a+b) = sin a cos b + sin b cos a, apply this to your problem with a = x, b = pi/2

Answer 2

is that sum and difference identity

Answer 3

did you have to take a selfie while popping that nasty zit? D:

Answer 4

@sourwing how'd you know?