What would this give: $\displaystyle \left[\frac{\cos n\pi t}{n \pi}\right]^0_{-1}$.

The solution given is $\displaystyle (1 + \cos n\pi)$.

I don't understand what to do with the $\displaystyle n\pi$ because $\displaystyle \cos(0) = 1$ but what does $\displaystyle \cos n\pi (0)$ equal? (Worried)