Show that z = r [cos() + i sin()] is the complex conjugate of z = r

Show that z̅ = r [cos(−θ) + i sin(−θ)] is the complex conjugate of z = r (cos θ + i sin θ )
Then find
(a) zz̅ and
(b) z / z̅, z̅ ≠ 0.