The formula for the area of a square is A = r2, where r is the side length of the square. Suppose a square is expanding, meaning that both the area 100 dA A and the side length r (in inches) are expanding. Suppose r = 2 - dA dr where t is time in seconds. Use the chain rule to (t + 7) 2 dt dr dt find the rate at which the area is expanding at t = 3 seconds