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."
Varsity Tutors
Varsity Tutors: Hotmath: Graphing Calculator Practice Problems Geometry
Practice using your graphing calculator for Geometry problems. If you get stumped or if you would like to check your work, then select the View Solution button, which is located directly under each problem.
Walter Fendt
Walter Fendt: Cyclic Quadrilateral (Inscribed Quadrilateral)
A short interactive activity which allows you to move the vertices of a quadrilateral to prove that the sum of the opposite angles is 180 degrees.