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WAEC Further Mathematics 2016 Question 21

Question 21

Trigonometry

Evaluate cos 75°, leaving the answer in a surd form.

  1. A.(√2/2)(√3 + 1)
  2. B.(√2/4)(√3 − 1)
  3. C.(√2/4)(√3 + 1)
  4. D.(√2/2)(√3 − 1)
Show the answer and explanation

Answer: B ((√2/4)(√3 − 1))

Explanation

cos(45° + 30°) = (√2/2)(√3/2) − (√2/2)(½) = (√2/4)(√3 − 1).