Question

establish the identity.
sin[x+ pi/2]=cos x

Answer 1

use formula for sin(A + B) = sin A cos B + sin B cos A

subsitute x for A; substitute pi/2 for B

Answer 2

pi\2 = 90 degree
so
sin(x+90)=cosx
taking left.hand.side
sin(a+b)=sinacosb+cosasinb
sin(x+90)= sinx cos 90 + cos x sin 90
since , sin 90=1 and cos 90=0
sin(x+90)=sinx(0) + cos x (1)
sin(x+90)= 0+cos x
sin(x+90)= cos x
hence proved

Answer 3

got it out thanks you guys!