The average rate of change (AROC) of a function f(x) on an interval [a, b] is equal to the slope of the secant line to the graph of f(x) that passes through (a, f(a)) and (b, f(b)), a.k.a. the difference quotient given by
![f_{\mathrm{AROC}[a,b]} = (f(b)-f(a))/(b-a)](https://img.qammunity.org/2023/formulas/mathematics/college/aillbfergkzesfevih43k61opmg862fr9j.png)
So for f(x) = x² on [1, 5], the AROC of f is
![f_{\mathrm{AROC}[1,5]} = (5^2-1^2)/(5-1) = \frac{24}4 = \boxed{6}](https://img.qammunity.org/2023/formulas/mathematics/college/6u0jbvipo1bygj95tvb8kznmwxfd5bsctl.png)