Answer
$a^{-4}\times a^{4}=1$
Work Step by Step
$a^{?}\times a^{4}=1$
The zero as an exponent rule states that for every nonzero number $a$, $a^0=1$.
Therefore, $a^{?}\times a^{4}=a^0$
To multiply powers with the same base, we add the exponents.
When we add $4$ and the first exponent, we must get $0$. The only way this is true is if the first exponent is $-4$ because $4+(-4)=0$.
Therefore, $a^{-4}\times a^{4}=a^0$
We rewrite the equation in its original form: $a^{-4}\times a^{4}=1$
