Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$-a^2+3a$
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}