If z=x+iyz = x+iyz=x+iy and w=u+ivw = u+ivw=u+iv, what is the real part of z⋅wz\cdot wz⋅w?
xu+yvxu+yvxu+yv
xu−yvxu-yvxu−yv
xv+yuxv+yuxv+yu