Chapter 6 - Section 6.1 - The Greatest Common Factor and Factoring by Grouping - Exercise Set - Page 427: 82

$(5x-6y)(2x+7y)$

Using factoring by grouping, the given expression, $ 10x^2-12xy+35xy-42y^2 ,$ is equivalent to \begin{array}{l}\require{cancel} (10x^2-12xy)+(35xy-42y^2) \\\\= 2x(5x-6y)+7y(5x-6y) \\\\= (5x-6y)(2x+7y) .\end{array}