Khan Academy: Geometry: Euler Line

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]

In this video tutorial [11:06], the instructor shows how to construct a two-column proof using triangle congruence postulates to prove that two line segments are perpendicular.

This video tutorial demonstrates solutions to problems #51-55 of the California Geometry released state test questions. Problems address proving and using the Pythagorean theorem and compass constructions. [12:35]

Demonstrates solutions to problems #56-60 of the California Geometry released state test questions. Problems address compass constructions, slope of perpendicular lines, and using the distance formula. [12:49]

Demonstrates solutions to problems #1-3 of California Geometry released state test questions. Problems address understanding of deductive reasoning and congruent angles created by parallel lines cut by a transversal. [10:17]

Demonstrates solutions to problems #7-10 of California Geometry released state test questions. Problems address understanding of congruent angle pairs when parallel lines are cut by a transversal, counterexamples, and properties of the...

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]

A video demonstration of the magic and mystery of the Euler Line.

Demonstrates solutions to problems #76-80 of California Geometry released state test questions. Problems address tangents to circles, secants to circles, intercepted arcs, translations on the coordinate plane, and rotations on the...

Demonstrates solutions to problems #71-75 of California Geometry released state test questions. Problems address Pythagorean theorem, 45-45-90 triangles, 30-60-90 triangles, circumscribed polygons, area, chord length, tangents to circles...