Question

The length of a rectangle is increasing at a rate of 3 cm/s and its width is increasing at a rate of 5 cm/s. when the length is 14 cm and the width is 9 cm, how fast is the area of the rectangle increasing?

Answer 1

area of rectangle = L * W

Differentiate with respect to time:

 dA
----- = L*(dW/dt) + W*(dL/dt)
 dt

Here, 

 dA
----- = (14 cm)*(5 cm/sec) + (9 cm)*(3 cm/sec)
 dt

Finish the indicated multiplication and addition to obtain your final answer.