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JAMB Mathematics 1990 Question 38

Question 38

Angles and Polygons

In a regular pentagon, PQRST, PR intersects QS at O. Calculate RÔS.

  1. A.36°
  2. B.72°
  3. C.108°
  4. D.144°
Show the answer and explanation

Answer: B (72°)

Explanation

Each interior angle is 108°, and the diagonals make 36° angles with the sides, so in triangle QOR the angles at Q and R are 36° each and angle QOR = 108°. RÔS is on a straight line with QOR, so it is 180° − 108° = 72°.