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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.
  • A.
    0.75cm2S-1
  • B.
    0.53cm2S-1
  • C.
    0.35cm2S-1
  • D.
    0.88cm2S-1
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

There is an explanation video available below.

Explanation Video

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