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  1. Chapter 2 Class 12 Inverse Trigonometric Functions
  2. Serial order wise

Transcript

Ex 2.2, 19 Find the values of cos−1(cos 7π/6) is equal to (A) 7π/6 (B) 5𝜋/6 (C) 𝜋/3 (D) 𝜋/6 Let y = cos−1 (cos 7π/6) cos y = cos (7π/6) cos y = cos (210°) We know that Range of principal value of cos is [0, π] i.e. [0° ,180°] Hence, y = 210° not possible Rough 7𝜋/6 = (7 × 180)/6 = 210° Now, cos y = cos (210°) cos y = cos (360° – 150°) cos y = cos (150°) cos y = cos ("150 × " 𝜋/180) cos y = cos (5𝜋/6) So, y = 5𝜋/6 Which is in the range of principal value of cos-1 i.e. [0,π] Hence , cos −1 (cos 7π/6) = y = 5𝜋/6 Thus, option (B) is correct (As cos (360 – θ) = cos θ)

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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.