If cos 60° = 1/2, which of the following angle has cosine of -1/2?

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Mathematics WAEC 1988

If cos 60° = 1/2, which of the following angle has cosine of -1/2?

  • 30o
  • 120o checkmark
  • 150o
  • 210o
  • 300o

The correct answer is: B

Explanation

cos 60° = 1/2, cos(180° - 60°) = -1/2

cos120° = -1/2

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