Answer
$ n=4 $ or $n=-4$.
Work Step by Step
By factorization, we have
$$4n^2-64=(2n+8)(2n-8)=0.$$
Then we have
$$(2n-8 ) =0, \quad \text{or} \quad (2n+8)=0$$
that is $ n=4 $ or $n=-4$.
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