Complex Numbers Exercise If $a,b,c$ are complex numbers with $a+b+c=0$ and $\|a\|=\|b\|=\|c\| = r>0$ then prove that $$a^{2^n} + b^{2^n} + c^{2^n} = 0$$
Any ideas?
Thanks! 

We have
$$
a + b + c = 0
$$
Taking the conjugate and multiplying by $abc$,
$$
abc \overline{a} + abc \overline{b} + abc \overline{c} = 0
$$
i.e.
$$
\newcommand{\abs}[1]{\left| #1 \right|}
bc \abs{a}^2 + ac \abs{b}^2 + ab \abs{c}^2
$$
But then $\abs{a} = \abs{b} = \abs{c}$, so
$$
ab + bc + ca = 0
$$
It follows that
$$
a^2 + b^2 + c^2 = (a + b + c)^2 - 2(ab + bc + ca) = 0
$$
In summary, we have shown that if $a + b + c = 0$ and $a, b, c$ have the same norm, $a^2 + b^2 + c^2 = 0$.
Since $a^2, b^2, c^2$ again have the same norm, it follows by induction that
$$
a^{2^n} + b^{2^n} + c^{2^n} = 0
$$
for all $n$.
