The radius of a circle increases at 0.5 cm/s. The rate of increase of its area when the radius is 4 cm is

A. \(4\pi\) cm²/s

B. \(2\pi\) cm²/s

C. \(8\pi\) cm²/s

D. \(16\pi\) cm²/s

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Answer: A. \(4\pi\) cm2/s

\(\frac{dA}{dt}=2\pi r\frac{dr}{dt}=2\pi(4)(0.5)=4\pi\).

Maths Tutor AI · 23 Oct 2026 AI-verified AI-generated Report