Khan Academy
Khan Academy: Triangles: Fill in the Blank Triangle Proofs Example 1
In this video, we listen to how a geometry exercise is completed as the presenter demonstrates the reasoning behind proving that the corresponding parts of triangles are congruent. [9:42]
Khan Academy
Khan Academy: Triangles: Proof: Triangle Altitudes Are Concurrent (Orthocenter)
Demostrates how to take any triangle and make it become the medial triangle of a larger triangle. Also explains that the three altitudes of a triangle are concurrent. [10:01]
Khan Academy
Khan Academy: Geometry: Part 1 of Proof of Heron's Formula
Demonstrates how to derive a version of Heron's formula using the Pythagorean Theorem and the formula for the area of a triangle. Applies Heron's formula to solve a sample problem. [10:59]
Khan Academy
Khan Academy: Geometry: Part 2 of the Proof of Heron's Formula
Completes the proof of Heron's formula that was begun in the video, "Part 1 of Proof of Heron's Formula." [12:08]
Khan Academy
Khan Academy: Geometry: Euler's Line Proof
Proves that the circumcenter, orthocenter, and centroid all lie on the same line, the Euler line. Proof relies on understanding of properties of similar triangles and properties of special parts of a triangle. [9:50]