[tex]\bf slope = m = \cfrac{rise}{run} \implies
\cfrac{ f(x_2) - f(x_1)}{ x_2 - x_1}\impliedby
\begin{array}{llll}
average~rate\\
of~change
\end{array}\\\\
-------------------------------\\\\
\begin{array}{ccll}
x&f(x)\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
-2&0\\2&15\\7&30
\end{array}
\qquad
\begin{cases}
x_1=2\\
x_2=7
\end{cases}\implies \cfrac{f(7)-f(2)}{7-2}\implies \cfrac{30-15}{5}
\\\\\\
\cfrac{15}{5}\implies 3[/tex]
