We will learn how to find the number of triangles contained in a polygon.
If the polygon has ‘n’ sides, then the number of triangle in a polygon is (n – 2).
In a triangle there are three sides. In the adjoining figure of a triangle ABC we can observe that the number of triangles contained = 3 – 2 = 1. 
In a quadrilateral there are four sides. Number of triangles contained in a quadrilateral = 4 – 2 = 2. In the adjoining figure of a quadrilateral ABCD, if diagonal BD is drawn, the quadrilateral will be divided into two triangles i.e. ∆ABD and ∆BDC. 
In a pentagon there are five sides. Number of triangles contained in a pentagon = 5 – 2 = 3. In the adjoining figure of a pentagon ABCDE, on joining AC and AD, the given pentagon is divided into three triangles i.e. ∆ABC, ∆ACD and ∆ADE. 
In a hexagon there are six sides. Number of triangles contained in a hexagon = 6 – 2 = 4.
In the adjoining figure of a hexagon ABCDEF, on joining AC, AD and AE, the given hexagon is divided into four triangles i.e. ∆ABC, ∆ACD, ∆ADE and ∆AEF. 
● Polygons
Polygon and its Classification
Interior and Exterior of the Polygon
Number of Triangles Contained in a Polygon
Angle Sum Property of a Polygon
Problems on Angle Sum Property of a Polygon
Sum of the Interior Angles of a Polygon
Sum of the Exterior Angles of a Polygon
7th Grade Math Problems
8th Grade Math Practice
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