Khan Academy: Geometry: Medians Divide Into Smaller Triangles of Equal Area

Showing that the three medians of a triangle divide it into six smaller triangles of equal area. Also a brief discussion of the centroid is given.

This video tutorial [9:00]explains how to find various measures of triangles formed by the medians of a right triangle. Based on the properties of the medians of a triangle, properties of centroids, and the Pythagorean theorem.

Proof that if the legs of an isosceles triangle are congruent then the base angles are congruent and vice versa using triangle congruency postulates. The proof is written as a two-column proof. [9:03]

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...

This video [7:50] demonstrates how to determine the area a regular hexagon with side length of 2 sq. rt. 3 based on knowledge of 30-60-90 triangles and the area formula of a triangle.

This video tutorial [15:15] provides a two-dimensional proof that the centroid is located two-thirds the way along every median of a triangle. This is a follow up to the proof in three-dimensions provided in the video, "Triangle Median...

This video tutorial [8:59] reviews the definitions of median and centroid in relation to a triangle and proves that the centroid is two-thirds the way along a median. The proof is done be drawing a triangle in three-dimensions.

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]

Explains how to determine unknown side lengths of similar triangles by identifying corresponding sides and angles ans setting up proportions. The first example is a continuation from the video "Similar Triangles." Practice problems...

Proves that the circumcenter of a right triangle is the midpoint of the hypotenuse. [5:42]