We have:
$a^1-b^1=a-b$
Since $a-b$ divides itself, the base case holds.
Now, let's assume that for some $k \in \mathbb{N}$, $(a-b) \mid (a^k-b^k)$.
We want to prove that $(a-b) \mid (a^{k+1}-b^{k+1})$.
We can start by expanding $a^{k+1}-b^{k+1}$ using the hint
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