Simplifcation of $e^{(-3 \pi i)/4}$

Question

I am trying to figure out how my textbook simplifies this:

$$\frac{1}{4}e^{(-3 \pi i)/4} = -\frac{1}{4}e^{(\pi i)/4}$$

I know that $e^{\pi i} = -1$ but what is going on here?

Answer 1

Multiply the left-hand side by $-e^{4\pi i/4} = -e^{\pi i} = 1$.