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JEE PYQ: Complex Numbers Question 21

Question 21 - 2020 (05 Sep Shift 2)

The value of $\left(\frac{-1+i\sqrt{3}}{1-i}\right)^{30}$ is:

(1) $-2^{15}$

(2) $2^{15}i$

(3) $-2^{15}i$

(4) $6^5$

Show Answer

Answer: (3)

Solution

$\frac{-1+i\sqrt{3}}{1-i} = \frac{2e^{i2\pi/3}}{\sqrt{2}e^{-i\pi/4}} = \sqrt{2}e^{i11\pi/12}$. Raised to 30th power: $(\sqrt{2})^{30}e^{i \cdot 30 \cdot 11\pi/12} = 2^{15}e^{i55\pi/2} = 2^{15}e^{i3\pi/2} = -2^{15}i$.


Learning Progress: Step 21 of 43 in this series