Chapter 1 - Some Basic Concepts of Arithmetic and Algebra - 1.5 - Use of Properties - Problem Set 1.5 - Page 34: 77

$34$

Combining like terms, the given expression, $ (a-b)-(a+b) ,$ simplifies to \begin{array}{l}\require{cancel} a-b-a-b \\\\= (a-a)+(-b-b) \\\\= 0-2b \\\\= -2b .\end{array} Substituting $ b=-17 ,$ the resulting expression above evaluates to \begin{array}{l}\require{cancel} -2(-17) \\\\= 34 .\end{array}