The radius of a circle is increasing at the rate of 0.02cms^-1. Find the rate at which the area is increasing when the radius of the circle is 7cm.

0.75cm²S^-1

0.53cm²S^-1

0.35cm²S^-1

0.88cm²S^-1

Correct answer is D

A = $\pi$ r², $\frac{\delta A}{\delta r}$ = 2πr

So, using $\frac{\delta A}{\delta t}$ = $\frac {\delta A}{\delta r}$ x $\frac {\delta A}{\delta t}$

= 2 $\pi$ r x 0.02

= 2 $\pi$ x 7 x 0.02

= 2 x $\frac{22}{7}$ x 0.02

= 0.88cm²s^-1

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