Write $\displaystyle -1+i $ in exponential form.

So far I have $\displaystyle \sqrt {2} [ ( - \cos ( \frac { \pi }{4} )+ i \sin ( \frac { \pi }{4}) ] $, but then how do I make it look like $\displaystyle \sqrt {2} e^ { i \frac { \pi }{4} } $? The minus sign in front of the cos is giving me problem here.

Thanks.