The radius of a circle is increasing at the rate of 0.02cms-1. Find the rate…

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.

Correct Answer: Option D

Explanation

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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