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Last updated at May 29, 2018 by Teachoo

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Ex 6.1,6 The radius of a circle is increasing at the rate of 0.7 cm/s. What is the rate of increase of its circumference? Let r be the radius of circle & C be the circumference of circle Given that Radius of a circle is increasing at the rate of 0.7 cm/sec i.e. ๐๐๏ทฎ๐๐ก๏ทฏ = 0.7 cm/sec We need find rate of change of circumference of circle w. r. ๐ก time i.e. we need to calculate ๐๐๏ทฎ๐๐ก๏ทฏ we know that Circumference of circle = 2ฯr i.e. C = 2ฯr Different w. r. t time ๐๐๏ทฎ๐๐ก๏ทฏ = ๐(2๐๐)๏ทฎ๐๐ก๏ทฏ ๐๐๏ทฎ๐๐ก๏ทฏ = 2ฯ ๐๐๏ทฎ๐๐ก๏ทฏ ๐๐๏ทฎ๐๐ก๏ทฏ = 2ฯ ร 0.7 ๐๐๏ทฎ๐๐ก๏ทฏ = 1.4 ฯ Since circumference is in cm & time is in sec ๐๐๏ทฎ๐๐ก๏ทฏ = 1.4ฯ ๐๐๏ทฎ๐ ๐๐๏ทฏ ๐๐๏ทฎ๐๐ก๏ทฏ = 1.4ฯ cm/sec Hence, circumference of circle is increasing at the rate of 1.4ฯcm/sec

Chapter 6 Class 12 Application of Derivatives

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Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.