Chapter 4 - Section 4.2 - Adding and Subtracting Polynomials - 4.2 Exercises - Page 285: 53

$8x^2+x-2$

Removing the grouping symbols and then combining like terms, the given expression, $ (5x^2+7x-4)+(3x^2-6x+2) ,$ simplifies to \begin{array}{l}\require{cancel} 5x^2+7x-4+3x^2-6x+2 \\\\= (5x^2+3x^2)+(7x-6x)+(-4+2) \\\\= 8x^2+x-2 .\end{array}