Instructional Video
Khan Academy

Khan Academy: Geometry: Inscribed and Central Angles

For Students 9th - 10th Standards
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]
Instructional Video
Massachusetts Institute of Technology

Mit: Blossoms: The Pythagorean Theorem: Geometry's Most Elegant Theorem

For Teachers 9th - 10th
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]
Instructional Video
Sophia Learning

Sophia: Proof (Harder)

For Students 9th - 10th
This geometry resource discusses two types of proof. Video lessons demonstrating a flow proof and a two-column proof are included.
Instructional Video
Sophia Learning

Sophia: Types of Proofs

For Students 9th - 10th Standards
Explore the similarities and differences between paragraph proofs, flow chart proofs, and two-column proofs. Assess learning with a quiz.
Instructional Video
Sophia Learning

Sophia: Introduction to Geometric Proof

For Students 9th - 10th Standards
Explore the structure and how to complete a flow proof and a two-column proof.
Instructional Video
Sophia Learning

Sophia: Intermediate Proof

For Students 9th - 10th Standards
Use the two-column proof and the flow proof to prove two triangles congruent.
Instructional Video
Sophia Learning

Sophia: Language of Geometry

For Students 9th - 10th
This video tutorial introduces some common terms for geometry including axiom, postulate, theorem, and corollary. Students can check their understanding with an assessment.
Instructional Video
Khan Academy

Khan Academy: Geometry: Part 2 of the Proof of Heron's Formula

For Students 9th - 10th Standards
Completes the proof of Heron's formula that was begun in the video, "Part 1 of Proof of Heron's Formula." [12:08]
Instructional Video
Khan Academy

Khan Academy: Geometry: Euler's Line Proof

For Students 9th - 10th Standards
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]
Instructional Video
Khan Academy

Khan Academy: Worked Examples: Geometry: Ca Geometry: Similar Triangles 1

For Students 9th - 10th
In this video tutorial students explore a proof using similar triangles.
Instructional Video
Khan Academy

Khan Academy: Triangles: Another Pythagorean Theorem Proof

For Students 9th - 10th Standards
Students explore the Pythagorean Theorem by exploring a visual proof of the Theorem as they watch a video tutorial.
Instructional Video
Khan Academy

Khan Academy: Triangles: Fill in the Blank Triangle Proofs Example 1

For Students 9th - 10th Standards
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]
Instructional Video
Sophia Learning

Sophia: Language of Geometry

For Students 9th - 10th Standards
This video lesson defines and provides an example of common geometry terms including theorem, postulate, axiom, and corollary.
Instructional Video
Khan Academy

Khan Academy: Geometry: Inradius Perimeter and Area

For Students 9th - 10th Standards
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]
Instructional Video
Khan Academy

Khan Academy: Geometry: Exploring Medial Triangles

For Students 9th - 10th
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.
Instructional Video
Khan Academy

Khan Academy: Geometry: Rhombus Diagonals

For Students 9th - 10th Standards
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]
Instructional Video
Khan Academy

Khan Academy: Geometry: Common Orthocenter and Centroid

For Students 9th - 10th Standards
Proves that if the orthocenter and centroid are the same point in a triangle then the triangle is a right triangle. [6:25]
Instructional Video
Khan Academy

Khan Academy: Geometry: Circumcenter of a Right Triangle

For Students 9th - 10th Standards
Proves that the circumcenter of a right triangle is the midpoint of the hypotenuse. [5:42]
Instructional Video
Loyola University Chicago

Math Flix: Similar Figures: Proof Using Proportions

For Students 9th - 10th Standards
This QuickTime movie provides an opportunity to develop the basic geometric term, similar, by checking to see if figures are proportionaly similar. As you watch and listen to the teacher and student interact it helps clarify the thinking...
Instructional Video
Sophia Learning

Sophia: Pythagorean Theorem Proof

For Students 9th - 10th Standards
Find the area of several figures to prove the Pythagorean theorem. Complete quiz to check understanding. [5:16]
Instructional Video
Study Pug

Study Pug: Perpendicular Line Proofs

For Students 9th - 10th Standards
Video lesson explains angles, lines, and transversals. [9:33]
Instructional Video
Sophia Learning

Sophia: Pythagorean Theorem Proof

For Students 9th - 10th Standards
Prove the Pythagorean theorem and take a quiz to assess learning.
Instructional Video
Khan Academy

Khan Academy: Geometry: Part 1 of Proof of Heron's Formula

For Students 9th - 10th Standards
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]
Instructional Video
Khan Academy

Khan Academy: Geometry: Angles of Parallel Lines 2

For Students 9th - 10th Standards
Explains how to determine the measures of all the angles formed when parallel lines are cut by a transversal based on the measure of one angle. Explains how to use corresponding congruent angles to determine if lines cut by a transversal...

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