Answer
$\dfrac{1}{a^{10}}$
Work Step by Step
Using the laws of exponents, the given expression, $
a^{-4}a^{-6}
,$ is equivalent to
\begin{array}{l}\require{cancel}
a^{-4+(-6)}
\\\\=
a^{-4-6}
\\\\=
a^{-10}
\\\\=
\dfrac{1}{a^{10}}
.\end{array}
For more complicated problems, it is helpful to remember that you can flip the location of numbers with negative exponents. In other words, you can move numbers with a negative exponent that are in the numerator to the denominator, and you can move numbers with a negative exponent in the denominator to the numerator.
