Chapter 9 - Roots and Radicals - Chapters 1-9 Cumulative Review Problem Set - Page 432: 8

$-49$

Removing the grouping symbols and then combining like terms, the given expression, $ (3x^2-4x-6)-(3x^2+3x+1) ,$ simplifies to \begin{array}{l}\require{cancel} 3x^2-4x-6-3x^2-3x-1 \\\\= (3x^2-3x^2)+(-4x-3x)+(-6-1) \\\\= -7x-7 .\end{array} Substituting $x=6$, the expression above evaluates to \begin{array}{l}\require{cancel} -7(6)-7 \\\\= -42-7 \\\\= -49 .\end{array}