#### Hckyplayer8

##### Junior Member

- Joined
- Jun 9, 2019

- Messages
- 235

The length of a rectangle is increasing at the rate of 5 m/min while the width is decreasing at the rate of 3 m/min. At a certain instant, the length is 20m and the width is 10m. At that instant determine the rate of change of the area and the rate of change of the perimeter.

First, the rate of of change of the area.

A = L times W. So of L=x and W=y, then dA/dt = (x) dy/dt + (y) dx/dt.

dx/dt= 5 m/min

dy/dt= -3 m/min

X=20m

Y=10m

dA/dt= x (-3) + y (5) = 20 (-3) + 10 (5) = -10m