Question

Find z1/z2 where

Z1 =20(cos 120° +isin 120°) and
z2 = 4(cos 30° + i sin 30°).

Answer 1

`\qquad \textit{division of two complex numbers} \\\\ \cfrac{r_1[\cos(\alpha)+i\sin(\alpha)]}{r_2[\cos(\beta)+i\sin(\beta)]}\implies \cfrac{r_1}{r_2}[\cos(\alpha - \beta)+i\sin(\alpha - \beta)] \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ z1=20[\cos(120^o)+i\sin(120^o)]~\hfill z2=4[\cos(30^o)+i\sin(30^o)] \\\\\\ \cfrac{z1}{z2}\implies \cfrac{20}{4}[\cos(120^o - 30^o)+i\sin(120^o - 30^o)]\implies 5[\cos(90^o)+i\sin(90^o)] \\\\\\ 5[0+i(1)]\implies 0+5i\implies \boxed{5i}`