If $n$ is an integer and $Z=\cos \theta+i \sin \theta, \theta \neq(2 n+1) \frac{\pi}{2}$, then $\frac{1+Z^{2…

If $n$ is an integer and $Z=\cos \theta+i \sin \theta, \theta \neq(2 n+1) \frac{\pi}{2}$, then $\frac{1+Z^{2 n}}{1-Z^{2 n}}=$
  1. $i \tan n \theta$
  2. $i \cot n \theta$
  3. $-i \tan n \theta$
  4. $-i \cot n \theta$

Solution

$Z=\cos \theta+i \sin \theta$
$\begin{aligned} & \frac{1+Z^{2 n}}{1-Z^{2 n}}=\frac{1+(\cos \theta+i \sin \theta)^{2 n}}{1-(\cos \theta+i \sin \theta)^{2 n}}=\frac{1+\cos 2 n \theta+i \sin 2 n \theta}{1-\cos 2 n \theta-i \sin 2 n \theta} \\ & =\frac{\cos n \theta}{i \sin n \theta}\left(\frac{\cos n \theta+i \sin n \theta}{-\cos n \theta-i \sin n \theta}\right)=i \cot n \theta\end{aligned}$

Asked in: AP EAMCET 2024 (21 May Shift 2)

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