Sophia Learning
Sophia: Using Triangles to Find the Sum of Interior Angles: Lesson 1
This lesson demonstrates how to use triangles to determine the sum of the interior angles of a polygon. It is 1 of 5 in the series titled "Using Triangles to Find the Sum of Interior Angles."
Curated OER
Science Kids: Science Images: Equilateral Triangle
This picture shows an equilateral triangle, a three sided regular polygon with internal angles of 60 degrees and sides of equal length.