Question

The height of a rectangle is increasing at a rate of 11 centimeters per hour and the width of the rectangle is decreasing at a rate of 9 centimeters per hour. At a certain instant, the height is 3 centimeters and the width is 8 centimeters. What is the rate of change of change of the area of the rectangle at that instant?​

Answer 1

Answer:

-39 cm²/h

Step-by-step explanation:

The area of the rectangle is A = hw where h = height and w = width.

So the rate of change of area with respect to time is

dA/dt = d(hw)/dt

dA/dt = hdw/dt + wdh/dt

Given that at an instant h = 3cm, w = 8 cm and dh/dt = + 11 cm/h and dw/dt = -9 cm/h(negative since it is decreasing)

So, dA/dt = hdw/dt + wdh/dt

dA/dt = 3 cm × (+11 cm/h) + 8 cm × (-9 cm/h)

dA/dt = 33 cm²/h - 72 cm²/h

dA/dt = -39 cm²/h