Question

Y=3cos(theta-pi/2)

Answer 1

Y = 3*cos (x - Pi/2).
Use the trig identity: cos (a - b) = cos a*cos b + sin a*sin b
y = 3cos (x - Pi/2) = 3cos x*cos Pi/2 + 3sin x*sin Pi/2
cos Pi/2 = 0, and sin Pi/2 = 1 --> y = 3*sin x