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

Answer:

Step-by-step explanation:

let length=l

width=w

Area A=lw

$\frac{dA}{dt}=l \frac{dw}{dt}+w \frac{di}{dt}\\\frac{dl}{dt}=8 cm/s\\\frac{dw}{dt}= 3 cm/s\\\frac{dA}{dt}=20 \times 3+10 \times 8=60+80=140 cm ^{2} /s$