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JAMB Mathematics 1981 Question 6

Question 6

Trigonometry

If sin x° = a/b, what is sin (90 − x)°?

  1. A.a/b
  2. B.1 − a/b
  3. C.√(b2 − a2)/b
  4. D.√(a2 − b2)/b
  5. E.√(b2 − a2)
Show the answer and explanation

Answer: C (√(b2 − a2)/b)

Explanation

sin(90 − x) = cos x. In a right triangle with opposite side a and hypotenuse b, the adjacent side is √(b² − a²), so cos x = √(b² − a²)/b.