If $\left(\frac{1-i}{1+i}\right)^{100}=a+i b$, where, $a b \in R$ and $i=\sqrt{-1}$, then $(a, b)$ is equal to

If $\left(\frac{1-i}{1+i}\right)^{100}=a+i b$, where, $a b \in R$ and $i=\sqrt{-1}$, then $(a, b)$ is equal to
  1. $(1,0)$
  2. $(0,1)$
  3. $(-1,2)$
  4. $(2,-1)$

Solution

$\begin{aligned} & \left(\frac{1-i}{1+i}\right)^{100}=\left\{\frac{(1-i)(1-i)}{(1+i)(1-i)}\right\}^{100}=\left(\frac{1-1-2 i}{1+1}\right)^{100}=(-i)^{100}=1=a+i b \\ & \Rightarrow a=1 \text { and } b=0\end{aligned}$

Asked in: MHT CET 2022 (10 Aug Shift 1)

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