Question

how to prove that
$\cos( \alpha ) = \frac{1}{2} ( {e}^{i \alpha } + {e}^{ - i \alpha } )$
​

Answer 1

First you need to do is solve a by simplifying both sides.
After you’ve done that you would need to keep the variable alone.
e
i
a
2
+
e
−
i
a
2
−
cos
(
a
)
=
0