Mr. Ohashi's Math 8 Website

Eighth Grade Math at Eckstein Middle School

Thursday, 6/8: Interior Angle Sums (Day 9 of 14)

Learning Target: Explore polygons to find a formula for the interior angle sum of any polygon.
Handouts: Interior Angle Sums (Turn in: Fri, 6/9)

Today we explored the interior angles of polygons. We know that the interior angles of any triangle always add up to 180 degrees. This is called an interior angle sum… because it is all of the interior angles added together (the sum!). Using our knowledge of triangles, we can then find the interior angle sum of any polygon by cutting the polygon up into triangles! To find the interior angle sums, pick a vertex (corner) and draw lines to other corners to form triangles. Since each triangle has 180 degrees in it, the interior angle sum of the polygon will be the number of triangles times 180 degrees.

We did the first part of the assignment together and found that there is a formula for finding this information without cutting up the shapes! If we take the number of sides of subtract 2, we know how many triangles are in the polygon. Then we can multiply that number of 180 to find the interior angle sum! We wrote that formula in our notes:

Your homework is to finish #1-5.


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