Answer
$3.915\times10^{-16}$
Work Step by Step
Using the laws of exponents and the concepts of scientific notation, the given expression, $
(8.7\times10^{-12})(4.5\times10^{-5})
$, simplifies to
\begin{array}{l}
(8.7)(4.5)\times10^{-12+(-5)}
\\\\=
39.15\times10^{-17}
\\\\=
3.915\times10^{-16}
.\end{array}