Example 1 Find the rate of change of the area of a circle per second with respect to its radius r when r = 5 cm.We have to find rate of change of area of circle with respect to radius i.e. we need to find (𝒅(𝑨𝒓𝒆𝒂 𝒐𝒇 𝒄𝒊𝒓𝒄𝒍𝒆))/(𝒅 (𝒓𝒂𝒅𝒊𝒖𝒔 𝒐𝒇 𝒄𝒊𝒓𝒄𝒍𝒆)) = 𝒅𝑨/𝒅𝒓 We know that Area of circle = π r2 A = πr2 Finding 𝒅𝑨/𝒅𝒓 𝑑𝐴/𝑑𝑟 = (𝑑(𝜋𝑟2))/𝑑𝑟 = π ((𝑟2))/𝑑𝑟 = π (2r) = 2πr For r = 5 cm 𝑑𝐴/𝑑𝑟 = 2π (5) = 10π cmx/s

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.