Hi, I am not seeing the following step:

We are given $\displaystyle cos(z)=\frac{e^{iz}+e^{-iz}}{2}=\frac{1}{2}$. Therefore,

$\displaystyle e^{2iz}-e^{iz}+1=0$, and sp by the quadratic formula....

I don't see how the got $\displaystyle cos(z)=\frac{e^{iz}+e^{-iz}}{2}=\frac{1}{2}$ into the form $\displaystyle e^{2iz}-e^{iz}+1=0$. I can see the mult. the 2 and subtracted $\displaystyle e^{iz}$ over, but I don't see how the got the $\displaystyle e^{2iz}$ term.

Thanks