Equivalent Trig Expression Question

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