JSS2 Third Term Mathematics Lesson Note – Angles in a Polygons

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WEEK  1

TOPIC: Angles in a polygon

(a) Types of polygons: convex, concave, regular, irregular

(b) Sum of interior angles in polygon (number of triangles in a polygon)

(c) Sum of exterior angles of a polygon

POLYGONS AND ITS TYPES

A closed plane figure bounded by straight lines (edges) is called a polygon. The number of sides of a polygon determines its names. The table below describes the names of polygons according to the number of their sides:

No. Of sides and angles	Polygon
3	Triangle
4	Quadrilateral
5	Pentagon
6	Hexagon
7	Heptagon
8	Octagon
9	Nonagon
10	Decagon
11	Undecagon / Hendecagon
12	Dodecagon
15	Pentadecagon
20	Icosagon

Types of Polygons

Convex Polygon: a convex polygon has all its interior angles pointing outwards. No angle is pointing inwards. Each internal angle of a convex polygon is always less than

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