WAEC - Mathematics (1999 - No. 8)
The interior angle of a regular polygon is twice the exterior angle. How many sides has the polygon?
5
6
8
9
Explication
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