Chapter 4 - Section 4.2 - Adding and Subtracting Polynomials - 4.2 Exercises - Page 285: 61

$-2a^2-2a-7$

Removing the grouping symbols and then combining like terms, the given expression, $ (2a^2+3a-1)-(4a^2+5a+6) ,$ simplifies to \begin{array}{l}\require{cancel} 2a^2+3a-1-4a^2-5a-6 \\\\= (2a^2-4a^2)+(3a-5a)+(-1-6) \\\\= -2a^2-2a-7 .\end{array}