Let [a, b] = the interval
The average rate of change can be found by using [f(b) - f(a)]/(b - a).
Let a = 1 and b = 5.
Let R = rate of change
17- x^2
R = [17 - 5^2] - [17 - 1^2]/(5 - 1)
R = [17 - 25] -[17 - 1]/4
R = [(-8) - (16)]/4
R = (-24)/4
R = -6
Done.