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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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