Grade 8 · Math
Find a polygon’s interior-angle sum practice
Use a triangle decomposition to find an angle sum.
Opening your practice adventure…
Try a sample
What is the sum in degrees of the interior angles of a 12-sided simple convex polygon?
- 1799
- 1801
- 1802
- 1800
See the answer & why
1800
Draw diagonals from one vertex to form 10 triangles. Their angles total 10 × 180 = 1800°.
A little hint: Divide the polygon into triangles from one vertex.
A teaching tip
A convex n-sided polygon can be divided into n−2 triangles from one vertex.