Answer
$-a^2+3a$
Work Step by Step
Removing the grouping symbols, then the given expression, $
(a^2-3a-2)-(2a^2-6a-2)
$, is equivalent to
\begin{array}{l}
a^2-3a-2-2a^2+6a+2
.\end{array}
By combining like terms, then
\begin{array}{l}
(a^2-2a^2)+(-3a+6a)+(-2+2)
\\\\=
-a^2+3a+0
\\\\=
-a^2+3a
.\end{array}