(a) $\frac{1 + i}{1 - i} = \frac{(1 + i)^{2}}{1 - i^{2}} = \frac{2i}{2} = i$ So, $\left( \frac{1 + i}{1 - i} \right)^{n} = (i)^{n}\ \Rightarrow \ n = 2$
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