Chapter 7 - Rational Functions - 7.3 Multiplying and Dividing Rational Expressions - 7.3 Exercises - Page 580: 12

$= -\frac{1}{4}$

$\frac{5(r+2)}{10r-70} \times \frac{4(7-r)}{8r+16}$ $= \frac{5(r+2)}{10(r-7)} \times \frac{4(7-r)}{8(r+2)}$ $= \frac{20(r+2)(7-r)}{80(r-7)(r+2)}$ $= \frac{20(r+2)(-(r-7))}{80(r-7)(r+2)}$ $= \frac{-20(r+2)}{80(r+2)}$ $= -\frac{20}{80}$ $= -\frac{2}{8}$ $= -\frac{1}{4}$