Question

The length of a rectangle is increasing at a rate of 8cm/s and its width is increasing at a rate of 3 cm/s. When the length is 20 cm and the width is 10 cm, how fast is the area of the rectangle increasing?

Answer 1

Explanation:

let length=l

width=w

Area A=lw

`(dA)/(dt)=l (dw)/(dt)+w (di)/(dt)\\(dl)/(dt)=8 cm/s\\(dw)/(dt)= 3 cm/s\\(dA)/(dt)=20 * 3+10 * 8=60+80=140 cm ^(2) /s`