JEE Main 2022MathematicsTrigonometric Ratios & IdentitiesMediumMCQ

JEE Main 2022 — Trigonometric Ratios & Identities Question with Solution

JEE Main 2022 (27 Jun Shift 1)

Question

The value of cos2π7+cos4π7+cos6π7 is equal to

Choose an option

Show full solutionCorrect option: B
Correct answer
B-12

Step-by-step explanation

Given, cos2π7+cos4π7+cos6π7

=12sinπ72cos2π7sinπ7+2cos4π7sinπ7+2cos6π7sinπ7

=12sinπ7sin3π7-sinπ7+sin5π7-sin3π7+sin7π7-sin5π7

Since, 2cosAsinB=sinA+B-sinA-B

=12sinπ7-sinπ7+sinπ

=-12, ∵sinπ=0

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About this question

This is a previous-year question from JEE Main 2022, covering the Trigonometric Ratios & Identities chapter of Mathematics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.