Find the difference quotient of $LaTeX: \displaystyle f(x)=- 2 x^{2} + 5 x + 8$ .

The difference quotient is $LaTeX: \displaystyle \frac{f(x+h)-f(x)}{h}$ . Evaluating $LaTeX: \displaystyle f(x+h)=5 h + 5 x - 2 \left(h + x\right)^{2} + 8$ and expanding gives $LaTeX: \displaystyle f(x+h)=- 2 h^{2} - 4 h x + 5 h - 2 x^{2} + 5 x + 8$ Evaluating the difference quotient gives $LaTeX: \displaystyle \frac{(- 2 h^{2} - 4 h x + 5 h - 2 x^{2} + 5 x + 8)-(- 2 x^{2} + 5 x + 8)}{h}$ Simplifying gives $LaTeX: \displaystyle \frac{- 2 h^{2} - 4 h x + 5 h}{h}=- 2 h - 4 x + 5$