Steps on how to do this would be massively appreciated...
cos ( θ + 3pi/2) = sin θ
We can use this identity to prove this
cos (A + B) = cosA*cosB - sinA*sinB
So we have
cosθ *cos 3pi/2 - sinθ * sin(3pi/2)
cosθ (0) - sinθ (-1)
0 + sinθ
sinθ