Which of the following is a fourth root of $$ \frac{1}{2}+\frac{i \sqrt{3}}{2} \text { ? } $$

Which of the following is a fourth root of $$ \frac{1}{2}+\frac{i \sqrt{3}}{2} \text { ? } $$
  1. $\operatorname{cis} \frac{\pi}{12}$
  2. $\operatorname{cis} \frac{\pi}{4}$
  3. $\operatorname{cis} \frac{\pi}{6}$
  4. $\operatorname{cis} \frac{\pi}{3}$

Solution

To Find 4th root of space $\frac{1}{2}+\frac{i \sqrt{3}}{2}$ $\begin{aligned} & \text { Let } Z=\frac{1}{2}+i \frac{\sqrt{3}}{2}=\cos \frac{\pi}{3}+i \sin \frac{\pi}{3} \\ & \left.\quad=e^{i^{\frac{\pi}{3}}} \quad \quad \quad \because e^{i \theta}=\cos \theta+i \sin \theta\right\} \\ & \therefore z^{\frac{1}{4}}=\left(e^{i \frac{\pi}{3}}\right)^{1 / 4}=e^{i \pi / 12} \text { or } \operatorname{cis} \frac{\pi}{12} \\ & \therefore \text { 4th root of } z \text { is cis } \frac{\pi}{12}\end{aligned}$

Asked in: AP EAMCET 2021 (25 Aug Shift 2)

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