POLYGONS


POLYGONS

The word polygon means having many sides. Therefore a closed plane figure made up of several line segments that are joined together is called a polygon.

For example, a triangle, a quadrilateral are polygons.

NB. A circle is not a polygon as it is not made of line segments.

Diagonals: The number of diagonals in a polygon of sides n is n(n-3)/2



Types of polygons
   
Regular polygons:  A polygons having all angles and all sides are equal is called a regular polygon.

Irregular polygons:  A polygon may have unequal angles and sides. Such polygons are called irregular polygon.

Name of polygons according to their sides

Name                               Number of sides

Triangle                                        3

Quadrilateral                               4

Pentagon                                       5

Hexagon                                        6

Heptagon                                       7

Octagon                                          8

Nonagon                                         9

Decagon                                        10

Types of angle of a polygon

Interior Angle:  angle formed by two adjacent sides inside the polygon.

Sum of Interior Angles in a Regular Polygon of Sides n is: 

(n-2) × 180 degree

Exterior Angle:  angle formed by two adjacent sides outside the polygon.

Sum of Exterior Angles in a Regular Polygon of Sides n is: 

360 degree

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