Home/
Competitive Exams/
JEE Main & Advanced/
Mathematics/
Trigonometry/
Question 200016
JEE Mathematics · Hard

Trigonometry: Identities MCQ

Solve this quality-checked JEE multiple-choice question, then review the correct answer and explanation.

Timer-based practiceDetailed answer reviewMobile-friendly flow
IdentitiesHardQuestion 200016

Question

The value of cos 20° cos 40° cos 80° is:
  1. A
    1/4
  2. B
    1/8
    Correct
  3. C
    1/2
  4. D
    √3/8

Correct answer

1/8

Explanation

Using the identity: cos θ cos(60°−θ) cos(60°+θ) = cos(3θ)/4. With θ = 20°: cos 20° cos 40° cos 80° = cos 60°/4 = (1/2)/4 = 1/8.

Review Trigonometry notesStart timed chapter practice