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Question: Answered & Verified by Expert
If $x+\frac{1}{x}=2 \cos \theta$, then $x$ is equal to
MathematicsComplex NumberJEE Main
Options:
  • A $\cos \theta+i \sin \theta$
  • B $\cos \theta-i \sin \theta$
  • C $\cos \theta \pm i \sin \theta$
  • D $\sin \theta \pm i \cos \theta$
Solution:
1315 Upvotes Verified Answer
The correct answer is: $\cos \theta \pm i \sin \theta$
$\begin{aligned} & x+\frac{1}{x}=2 \cos \theta \Rightarrow x^2-2 x \cos \theta+1=0 \\ & \Rightarrow x=\frac{2 \cos \theta \pm \sqrt{4 \cos ^2 \theta-4}}{2} \Rightarrow x=\cos \theta \pm i \sin \theta\end{aligned}$

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