Find the difference quotient of $LaTeX: \displaystyle f(x)=9 - 2 x$ .

The difference quotient is $LaTeX: \displaystyle \frac{f(x+h)-f(x)}{h}$ . Evaluating $LaTeX: \displaystyle f(x+h)=- 2 h - 2 x + 9$ and expanding gives $LaTeX: \displaystyle f(x+h)=- 2 h - 2 x + 9$ Evaluating the difference quotient gives $LaTeX: \displaystyle \frac{(- 2 h - 2 x + 9)-(9 - 2 x)}{h}$ Simplifying gives $LaTeX: \displaystyle \frac{- 2 h}{h}=-2$