Use the difference quotient of A(r)= πr2 to calculate the average rate of change during certain intervals. The difference quotient of A(r) is:

StartFraction pi (r + h) squared minus pi r squared Over h EndFraction = StartFraction pi (r squared + 2 r h + h squared) minus pi r squared Over h EndFraction = StartFraction pi r squared + 2 pi r h + pi h squared minus pi r squared Over h EndFraction = 2 pi r + pi h

The average rate of change from the interval 2 to 3 inches is
π square inches per inch.

The average rate of change from the interval 2 to 2.5 is
π square inches per inch.