Suppose that the distance D feet that a car travels in t seconds is given by d (t) = 2t^2. Calculate the average speed (average rate of change.) in feet per second from t=5 to t=9. (An exact number.)

d (t) = 2t^2. [5,9]

The average rate of change is calculated by the formula: d (t2) - d (t1) / t2 - t1

So plug in 5 as t1 and 9 as t2.

d (9) - d (5) / 9 - 5 =

(2*81) - (2*25) / 9 - 5 =

162 - 50 / 4 =

112 / 4 = 28

The average speed is 28 feet.