average rate of change

Question

given the function f(x)=x^2+12x. find the average rate of change as x changes from 3 to 5

Answer 1

The average rate of change is the slope of the straight line connecting the endpoints of the interval: (3,f(3)) and (5,f(5))

f(x) = x² + 12x

f(3) = 3² + 12·3 = 9 + 36 = 45

f(5) = 5² + 12·5 = 25 + 60 = 85

The slope formula is:

slope = average rate of change = ( f(5) - f(3) ) / (5-3) = ____?