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Question 200044
JEE Mathematics · Hard

Trigonometry: Product MCQ

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

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ProductHardQuestion 200044

Question

cos 36° − cos 72° equals:
  1. A
    1/2
    Correct
  2. B
    1
  3. C
    √5/4
  4. D
    1/4

Correct answer

1/2

Explanation

cos 36° = (√5+1)/4 × 2 = (1+√5)/4. cos 72° = (√5−1)/4 × 2. cos36° − cos72° = [(1+√5)−(√5−1)]/4 = 2/4 = 1/2.

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