The interior angle of a regular polygon is twice the exterior angle. How many sides has the polygon?

  • A 5
  • B 6
  • C 8
  • D 9
waec 1999mathematics

The correct answer is B. 6

Let the exterior angle = d

Note: Exterior angle + Interior angle = 180°

\(\implies\) d + 2d = 180°

3d = 180° \(\implies\) d = 60°

Recall, exterior angle = \(\frac{360}{\text{no of sides}}\)

\(\therefore \text{No of sides} = \frac{360}{60}\)

= 6 sides

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