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WAEC Mathematics 2021 Question 23

Question 23

Trigonometry

If tan θ = 3/4, 180° < θ < 270°, find the value of cos θ.

  1. A.4/5
  2. B.3/5
  3. C.−4/5
  4. D.−3/5
Show the answer and explanation

Answer: C (−4/5)

Explanation

From a 3-4-5 triangle, |cos θ| = 4/5. In the third quadrant cosine is negative, so cos θ = −4/5.