cos(3π/2 + π/3) cos(π/3)+ sin(3π/2 + π/3) sin(π/3)
=cos(π/3-π/2)cos(π/3)+sin(π/3-π/2)sin(π/3)
=sin(π/3)cos(π/3)-cos(π/3)sin(π/3)
=0
cos(3π/2 + π/3) cos(π/3)+ sin(3π/2 + π/3) sin(π/3)
=(cos(3π/2)cos(π/3)-sin(3π/2)sin(π/3))cos(π/3)+(sin(3π/2)cos(π/3)+cos(3π/2)sin(π/3))sin(π/3)
=sin(π/3)cos(π/3)-cos(π/3)sin(π/3)
=0
