###### Definition4.3.12Rate of Change

If $$\left(x_1,y_1\right)$$ and $$\left(x_2,y_2\right)$$ are two data points from a set of two-variable data, then the rate of change between them is

\begin{equation*} \frac{\text{change in $y$}}{\text{change in $x$}}=\frac{\Delta y}{\Delta x}=\frac{y_2-y_1}{x_2-x_1}\text{.} \end{equation*}

(The Greek letter delta, $$\Delta\text{,}$$ is used to represent “change in” since it is the first letter of the Greek word for “difference”.)

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