Given two complex numbers z1=r1(cos θ1+ i sin θ1) and z2=r2(cos θ2+ i sin θ2), prove the following formula for the division of complex numbers. z1/z2=r1/r2 [cos (θ1− θ2) + i sin (θ1− θ2)] Show that the product of z = r[cos(- θ) + i sin(- θ)] and z = r(cos θ + i sin θ ) is equal to the square of the modulus.