Introduction In the previous post, we have shown that the sum of the interior angles of a polygon with sides is degrees. In this post, we explore the exterior angles of a polygon. The exterior angle is formed by extending the side of the polygon as shown in the following figure. One observation about the exterior […]

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# Monthly Archives: November 2012

## The Proof of the Polygon Angle Sum Theorem

Introduction We have learned that the angle sum of a triangle is . We have also learned that the angle sum of a quadrilateral is . In getting the angle sum of quadrilaterals, we divided the quadrilateral into two triangles by drawing a diagonal. In this post, we use this method to find the angle […]

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## Proof of Angle Sum of Quadrilaterals

Introduction We have learned that the angle sum of a triangle is . What about the quadrilaterals? The square and the rectangles have four right angles, so clearly, the sum of their interior angles is . But what about other quadrilaterals? Before proceeding with the proof, to those who want to explore first, draw different […]

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