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The Exterior Angle of a Regular Polygon is One-third of Its Interior Angle. Find the Number of Sides of the Polygon. - Mathematics

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Question

The exterior angle of a regular polygon is one-third of its interior angle. Find the number of sides of the polygon.

Sum

Solution

Let the interior angle be x

Then, the exterior angle is `x/(3)`

∴ `x + x/(3)` = 180°  ...[Interior angle and exterior angle form a linear pair]

⇒ `(4x)/(3)` = 180°

⇒ x = `(3)/(4) xx 180°`
= 135°

∴ Exterior angle

= `(135°)/(3)`
= 45°

Each exterior angle

= `(360°)/"n"`

⇒ `(360°)/"n"` = 45°
⇒ n = 8
∴ the regular polygon has 8 sides.

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Names of Polygons
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Chapter 18: Rectilinear Figures - Exercise 18.1

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Frank Mathematics [English] Class 9 ICSE
Chapter 18 Rectilinear Figures
Exercise 18.1 | Q 29
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