Explanation
If $$A=\left ( \begin{matrix}cos \theta & isin\theta \\isin \theta & cos\theta\end{matrix} \right )$$, where $$ i =\sqrt { - 1} $$, then by principle of Mathematical Induction then $$ A^n=\left [ \begin{matrix}cos\,n \theta & isin\,n \theta \\isin\,n\theta & cos\,n \theta\end{matrix} \right ]$$.
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