Recall that the average rate of change quantifies how much the y variable changes with respect the change on the x variable. That is, how much the dependent variable as the independent variable changes. If we consider the independent variable as an input, the dependent variable would be an output. Thus, the average rate of change would be
![\frac{change\text{ in output}}{change\text{ in input}}]()
using the delta notation, and considering y as the output and x as the input, we get
Now, consider