Check sibling questions

Ex 2.2, 19 (MCQ) - Chapter 2 Class 12 Inverse Trigonometric Functions (Term 1)

Last updated at March 30, 2023 by

Ex 2.2, 19 - Find cos-1(cos 7pi/6) is equal to (A) 7pi/6

Ex 2.2, 19 - Chapter 2 Class 12 Inverse Trigonometric Functions - Part 2

Get live Maths 1-on-1 Classs - Class 6 to 12

Book 30 minute class for ₹ 499 ₹ 299

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°) Since Range of of cos−1 is [0, π] i.e. [0° ,180°] Hence, y = 210° not possible Now, cos y = cos (210°) cos y = cos (360° – 150°) cos y = cos (150°) cos y = cos (𝟓𝝅/𝟔) Hence, y = 𝟓𝝅/𝟔 Which is in the range of principal value of cos-1 i.e. [0, π] Hence , cos −1 (cos 7π/6) = 5𝜋/6 Thus, option (B) is correct (As cos (360° – θ) = cos θ)

Ask a doubt
Davneet Singh's photo - Co-founder, Teachoo

Made by

Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.