# Ex 6.1,17 - Chapter 6 Class 12 Application of Derivatives

Last updated at May 29, 2018 by Teachoo

Last updated at May 29, 2018 by Teachoo

Transcript

Ex 6.1,17 The rate of change of the area of a circle with respect to its radius r at r = 6 cm is (A) 10p (B) 12p (C) 8p (D) 11p Let r be the radius of circle & A be the area of circle We need to find Rate of change of Area of circle w.r.t to radius at ๐ = 6 i.e. we need to find ๐๐ด๏ทฎ๐๐๏ทฏ at ๐ = 6 We know that Area of circle = ๐ ๐๏ทฎ2๏ทฏ i.e. A = ๐ ๐๏ทฎ2๏ทฏ Diff w.r.t ๐ ๐๐ด๏ทฎ๐๐๏ทฏ= ๐ ๐ ๐๏ทฎ2๏ทฏ๏ทฏ๏ทฎ๐๐๏ทฏ ๐๐ด๏ทฎ๐๐๏ทฏ=๐ ๐ ๐๏ทฎ2๏ทฏ๏ทฏ๏ทฎ๐๐๏ทฏ ๐๐ด๏ทฎ๐๐๏ทฏ=๐ . 2r ๐๐ด๏ทฎ๐๐๏ทฏ=2๐๐ We need to ๐๐ด๏ทฎ๐๐๏ทฏ when ๐ = 6 ๐๐ด๏ทฎ๐๐๏ทฏโ๏ทฎ๐ = 6 ๏ทฏ=2๐ 6๏ทฏ ๐๐ด๏ทฎ๐๐๏ทฏโ๏ทฎ๐ = 6 ๏ทฏ=12๐ Hence correct answer is B

Chapter 6 Class 12 Application of Derivatives

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