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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