4-1.Complex numbers
easy

If $z = \frac{{ - 2}}{{1 + \sqrt 3 \,i}}$ then the value of $arg\,(z)$ is

A

$\pi $

B

$\pi /3$

C

$2\pi /3$

D

$\pi /4$

Solution

(c)$z = \frac{{ – 2}}{{1 + \sqrt 3 i}}$=$\frac{{ – 2}}{{1 + \sqrt 3 i}} \times \frac{{1 – \sqrt 3 i}}{{1 – \sqrt 3 i}}$$ = \frac{{ – 2 + 2\sqrt 3 i}}{{1 + 3}}$
$ \Rightarrow z = \frac{{ – 1}}{2} + \frac{{\sqrt 3 }}{2}i$

$ \Rightarrow \,arg\,(z) = {\tan ^{ – 1}}\left( { – \frac{{\sqrt 3 /2}}{{1/2}}} \right) = \frac{{2\pi }}{3}$.

Standard 11
Mathematics

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