I read that

$1\over{2}$$\pi$$i$($\exp[-3i\pi/4]+\exp[-9i\pi/4])$

= $1\over{2}$$\pi$$i$($-\exp[i\pi/4]+\exp[-i\pi/4])$

= $\pi$$\sin(\pi/4)$ = $\pi\sqrt{2}$

Can you help me to understand how we move from the first line to the second?

Thanks.