Khan Academy: Geometry: Triangle Angle Example 2

Explains how to solve for multiple missing angles in a diagram composed of multiple triangles using the triangle sum theorem and other angle relationships. This video also appears in the Geometry: Triangles strand. [5:42]

Explains how to use the triangle sum theorem to solve for missing angle measures in a triangle. Also addresses the relationship between the measure of an exterior angle of a triangle and the measures of the remote interior angles. This...

Proof that the sum of the angles in a triangle is 180 using the relationship of angles formed when parallel lines are cut by a transversal. This video also appears in the Geometry: Triangles strand. [6:31]

Don't believe everything that you hear — make them prove it! The video shows two methods to prove the Triangle Angle Sum Theorem. The following two videos apply the theorem to finding missing angle measures.

Use the Angle Bisector Theorem to find missing side lengths in triangles. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.

Explains how to use given algebraic expressions for the measures of angles in an isosceles triangle and apply knowledge of the triangle sum theorem and the knowledge that the base angles of an isosceles triangle are congruent to...

Solving for unknown angle measures using knowledge of different angle relationships and the triangle sum theorem. [9:01]

Proof by contradiction that if two lines cut by a transversal create congruent corresponding angles then the lines are parallel. [5:18]

Use the angle bisector theorem to find missing side lengths in triangles.

A continuation of the video Limit Examples (Part 1), also from the Khan Academy. Addresses the case where the limit of a function is equal to infinity. Examples are explained both graphically and tabularly. [6:58]