I am trying to follow a solution to a problem and it says that $\left(\frac{1+i\tan\theta}{1-i\tan\theta}\right)^a = \left(\frac{\cos\theta+i\sin\theta}{\cos\theta-i\sin\theta}\right)^a$
However, I am unable to see why this would be? It is probably just a simple oversight but I am unsure.