Khan Academy
Khan Academy: Geometry: Point Line Distance and Angle Bisectors
Proof that a point on the angle bisector is equidistant from each side of the angle and proof that a point that is equidistant from each side of the angle lies on the angle bisector. [10:57]
Khan Academy
Khan Academy: Geometry: Triangle Area Proofs
Proof that the area of any triangle is half the product of the base and the height. Three different types of triangles are used to prove the formula. [10:23]
Khan Academy
Khan Academy: Geometry: Proof Vertical Angles Are Equal
Proof that the measures of vertical angles are equal based on properties of supplementary angles. [4:51]
Khan Academy
Khan Academy: Geometry: Congruent Triangle Example 2
Demonstrates how to use triangle congruency to prove that corresponding sides of congruent triangles are congruent and then identifies other congruent parts in the overlapping triangle diagram. The proof is written in the form of a...
Khan Academy
Khan Academy: Geometry: Triangle Medians and Centroids
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.
Khan Academy
Khan Academy: Geometry: Inscribed and Central Angles
Proof that the measure of an inscribed angle is half the measure of a central angle when the angles intercept the same arc. [14:16]
Sophia Learning
Sophia: Proof (Harder)
This geometry resource discusses two types of proof. Video lessons demonstrating a flow proof and a two-column proof are included.
Sophia Learning
Sophia: Language of Geometry
This video tutorial introduces some common terms for geometry including axiom, postulate, theorem, and corollary. Students can check their understanding with an assessment.
Khan Academy
Khan Academy: Worked Examples: Geometry: Ca Geometry: Proof by Contradiction
Students explore how to do a geometric proof by contradiction.
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]
Khan Academy
Khan Academy: Worked Examples: Geometry: Ca Geometry: Similar Triangles 1
In this video tutorial students explore a proof using similar triangles.
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]
Sophia Learning
Sophia: Language of Geometry
This video lesson defines and provides an example of common geometry terms including theorem, postulate, axiom, and corollary.
Khan Academy
Khan Academy: Geometry: Inradius Perimeter and Area
Proof that the area of a triangle is equal to half the inradius times the perimeter of the triangle, or the area is equal to the inradius times the semiperimeter. This video also appears in the Geometry: Circles strand. [7:29]
Khan Academy
Khan Academy: Geometry: Exploring Medial Triangles
This video tutorial [11:32] explains what a medial triangle is and proves that the medial triangle divides the original triangle into four congruent triangles. Proof uses triangle similarity and triangle congruence postulates.
Khan Academy
Khan Academy: Geometry: Proof Rhombus Area Half Product of Diagonal Length
Demostrates how to prove that one way to find the area of a rhombus is by taking half the product of the diagonals. [5:07]
Khan Academy
Khan Academy: Geometry: Proof Rhombus Diagonals Are Perpendicular Bisectors
Demonstrates how to prove that the diagonals of a rhombus are perpendicular bisectors of each other based on knowledge of properties of parallelogram diagonals, triangle congruency, and supplementary angles. [4:04]
Massachusetts Institute of Technology
Mit: Blossoms: The Pythagorean Theorem: Geometry's Most Elegant Theorem
Use this video to help teach the Pythagorean Theorem. The video can be downloaded, there is a transcript of the video, and a teacher's guide to aid in using the video. [21:38]
Khan Academy
Khan Academy: Geometry: Rhombus Diagonals
Demonstrates how to prove that the diagonals of a rhombus are perpendicular bisectors of each other based on knowledge of triangle congruency postulates and properties of altitudes. [4:38]
Khan Academy
Khan Academy: Geometry: Common Orthocenter and Centroid
Proves that if the orthocenter and centroid are the same point in a triangle then the triangle is a right triangle. [6:25]
Khan Academy
Khan Academy: Geometry: Circumcenter of a Right Triangle
Proves that the circumcenter of a right triangle is the midpoint of the hypotenuse. [5:42]
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