Proof of $(ab)^n=a^nb^n$ is fulfilled when it is true for $n = 2$

Question

Prove that for given elements $a,b$ from group $G$, equation $(ab)^n = a^nb^n$ is fulfilled for all $n∈ {\displaystyle \mathbb {Z} }, $ if and only if equation is true for $ n=2 $.

I have no idea how to prove it. I would be gratefulfor any help.