Question

The length of a rectangle is increasing at a rate of 9 cm/s and its width is increasing at a rate of 4 cm/s. When the length is 15 cm and the width is 12 cm, how fast is the area of the rectangle increasing

Answer 1

Answer:

The area of the rectangle is increasing at a rate of 168 square centimeters per second.

Step-by-step explanation:

Geometrically speaking, the area of a rectangle ($A$), in square centimeters, is described by following expression:

$A = w\cdot l$ (1)

Where:

$w$ - Width, in centimeters.

$h$ - Height, in centimeters.

By Differential Calculus, we find an expression for the rate of change of the area of the rectangle ($\dot A$), in square centimeters per second:

$\dot A = \dot w\cdot l + w\cdot \dot l$ (2)

Where:

$\dot w$ - Rate of change of the width of the rectangle, in centimeters per second.

$\dot l$ - Rate of change of the length of the rectangle, in centimeters per second.

If we know that $w = 12\,cm$, $l = 15\,cm$, $\dot w = 4\,\frac{cm}{s}$ and $\dot l = 9\,\frac{cm}{s}$, then the rate of change of the area of the rectangle is:

$\dot A = \dot w\cdot l + w\cdot \dot l$

$\dot A = 168\,\frac{cm^{2}}{s}$

The area of the rectangle is increasing at a rate of 168 square centimeters per second.