## Intermediate Algebra (6th Edition)

$-1$
Factoring the expressions and then cancelling the common factor/s between the numerator and the denominator, the given expression, $\dfrac{x-12}{12-x} ,$ simplifies to \begin{array}{l}\require{cancel} \dfrac{-1(-x+12)}{12-x} \\\\= \dfrac{-1(12-x)}{12-x} \\\\= \dfrac{-1(\cancel{12-x})}{\cancel{12-x}} \\\\= -1 .\end{array}