<s>[INST] Solve $e^{2z} - 2e^z + 2= 0$ So I've started by looking at
\begin{align} e^{z} =  x:\\
x^2 - 2x + 2 = 0
\end{align}
Whose solutions should be: \begin{align}\ 1+i, 1-i \end{align}
Then I did the following:
\begin{align}
e^z=e^{x+iy}=e^x(\cos y+i\sin y)&=\cos\frac{\pi}{4}+i\sin\frac{\pi}{4}=\frac{1}{2}+\frac{i \cdot 1}{2}\\
e^x= {\sqrt{2}} \quad \text{and}\quad y&=\frac{\pi}{4}+2\pi k\quad k \in \Bbb{Z}\\
x&= \sqrt{2} \quad \text{and} \quad y=\frac{\pi}{4}\\
\text{Also,} \quad e^x(\cos y+\sin y)&=\cos(\frac{7\pi}{4})+i\sin\frac{7\pi}{4})=\frac{1}{2}-\frac{i \cdot 1}{2}\\
e^x= \sqrt{2} \quad \text{and}\quad y&=\frac{7\pi}{4}+2\pi k\quad k \in \Bbb{Z}\\
x&= \sqrt{2} \quad \text{and} \quad y=\frac{7\pi}{4}\\
\end{align}
Are the solutions the following? \begin{align} \sqrt{2} + \frac{\pi}{4} \quad \text{and} \quad \sqrt{2} + \frac{7\pi}{4} \end{align}
Forgive the shoddy formatting as this is my first ever post here. Thanks.
 [/INST] Yes, the solutions of $x^2-2x+2=0$ are $1+i$ and $1-i$. So, the solutions of $e^{2z}-2e^z+2=0$ are all those numbers $z$ such that $e^z=1+i$ or that $e^z=1-i$. But$$1+i=\sqrt2\left(\frac1{\sqrt2}+\frac i{\sqrt2}\right)=\sqrt2e^{\pi i/4}. $$Therefore$$e^z=1+i\iff z=\log\sqrt2+\frac{\pi i}4+2\pi in,$$for some $n\in\Bbb Z$. The case of the equality $e^z=1-i$ is similar.
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