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WAEC Mathematics 2008 Question 46

Question 46

Triangles and Quadrilaterals

In the diagram, find the size of the angle marked a°.

Diagram for this question
  1. A.60°
  2. B.80°
  3. C.120°
  4. D.160°
Show the answer and explanation

Answer: B (80°)

Explanation

The reflex angle at O is 280°, so ∠ROT inside the shape is 80° and the angle at S on the circle is ½ × 280° = 140°. The four angles of RO TS add to 360°: 60 + 80 + 140 + a = 360, so a = 80°.