Last updated at May 29, 2018 by Teachoo

Transcript

Ex 2.2, 19 Find the values of cos-1(cos 7ฯ/6) is equal to (A) 7ฯ/6 (B) 5๐/6 (C) ๐/3 (D) ๐/6 Let y = cos โ1 (cos 7ฯ/6) cos y = cos (7ฯ/6) cos y = cos (210ยฐ) We know that range of principal value of cos is [0,ฯ] i.e. [0ยฐ ,180ยฐ] Hence y = 210ยฐ not possible Now, cos y = cos (210ยฐ) cos y = cos (360ยฐ โ 150ยฐ) cos y = cos (150ยฐ) cos y = cos (150 ร ๐/180) cos y = cos (5๐/6) y = 5๐/6 Which is in the range of principal value of cos-1 i.e. [0,ฯ] Hence , cos โ1 (cos 7ฯ/6) = y = 5๐/6 Thus, option (B) is correct

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Chapter 2 Class 12 Inverse Trigonometric Functions

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About the Author

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.