Dividing Polygons into Triangles (Part 1)
geometry · interior angle sums of quadrilaterals and pentagons
Use triangle angle sums to figure out the sum of the angle measurements in regular polygons.
Dividing Polygons into Triangles (Part 1) is a Grade 8 geometry investigation that uses the 180° angle sum of a triangle to reason about quadrilaterals and pentagons. Students draw diagonals from vertices, partition polygons into triangles, and use the number of triangles to determine the total interior angle measure. The construction makes the angle sum something students derive rather than memorize.
Use it as a whole-class exploration before introducing a general polygon formula. Ask students to explain why a quadrilateral makes two triangles and a pentagon makes three. Generate teacher-ready lesson support for Dividing Polygons into Triangles (Part 1) with a free Find a Math Game account. No credit card; 3 lifetime generations.
- Grades:
- 8
- Classroom use:
- whole class
Standards alignment
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