Question

What is the value of the expression $8^{-2}$

Answer 1

Simple...

$\frac{1}{64}$

or 0.015625

Thus, your answer.

Answer 2

$a^{-n}=\dfrac{1}{a^n}\ for\ a\neq0\\\\8^{-2}=\dfrac{1}{8^2}=\dfrac{1}{64}$