Question

the area of a square whose sides have length x cm is increasing at the rate of 12cm²/s. how fast is the length of a side increasing when the area is 81cm²​

Answer 1

Answer:

0.67 cm/s

Step-by-step explanation:

The area of a square is given by :

$A=x^2$ ....(1)

Where

x is the side of a square

$\dfrac{dA}{dt}=12\ cm^2/s$

Differentiating equation (1) wrt t.

$\dfrac{dA}{dt}=2x\times \dfrac{dx}{dt}$

When A = 81cm²​, the side of the square, x = 9 cm

Put all the values,

$12=2\times 9\times \dfrac{dx}{dt}\\\\\dfrac{dx}{dt}=\dfrac{2}{3}\\\\\dfrac{dx}{dt}=0.67\ cm/s$

So, the length of the side of a square is changing at the rate of 0.67 cm/s.