(a) Find the average rate of change of the area of the circle with respect to its radius $r$ as $r$ changes from:
(i) 2 to 3, (ii) 2 to 2.5, (iii) 2 to 2.1

(b) Find the instantaneous rate of change when $r=2$. [Do you notice anything interesting about the formula of $dA/dr$?]

(b)$A'(2)=$