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JAMB Mathematics 2001 Question 25

Question 25

Mensuration of Plane Shapes

The chord ST of a circle is equal to the radius, r, of the circle. Find the length of arc ST.

  1. A.πr/2
  2. B.πr/3
  3. C.πr/6
  4. D.πr/12
Show the answer and explanation

Answer: B (πr/3)

Explanation

A chord equal to the radius forms an equilateral triangle with the centre, so it subtends 60°. Arc length = (60/360) × 2πr = πr/3.