Answer
$e^{\pi i}+1=0$
Work Step by Step
We are given that $e^{a+ib}=e^a (\cos b+i \sin b)$
Plug $a=0; b=\pi$
$e^{0+\pi i}=e^{0} (\cos \pi+i \sin \pi)$
This gives: $e^{\pi i}=-1+0$
and $e^{\pi i}+1=0$
Hence, the result has been proved.