(iii) z1⋅z2z_1\cdot z_2z1⋅z2 z1z2=77(cos5π6+isin5π6)z_1z_2=77\left(\cos\frac{5\pi}{6}+i\sin\frac{5\pi}{6}\right)z1z2=77(cos65π+isin65π) cos5π6=−32,sin5π6=12\cos\frac{5\pi}{6}=-\frac{\sqrt{3}}{2},\quad \sin\frac{5\pi}{6}=\frac{1}{2}cos65π=−23,sin65π=21 z1z2=−7732+772i\boxed{z_1z_2=-\frac{77\sqrt{3}}{2}+\frac{77}{2}i}z1z2=−2773+277i