Khan Academy
Rhombus Diagonals, Quadrilaterals, Geometry
Delving into proof that the diagonals of a rhombus are perpendicular to each other, this lecture evaluates the angles and sides of this figure. It would serve as a great test preparation activity.
Brightstorm
Triangle Angle Sum
Don't believe everything that you hear — make them prove it! The video shows two methods to prove the Triangle Angle Sum Theorem. The following two videos apply the theorem to finding missing angle measures.
CK-12 Foundation
Alternate Interior Angles: Lesson
Concepts of alternate interior angles parallel the concepts of corresponding angles. Using a diagram, the presentation defines and identifies alternate interior angles formed by a transversal and two parallel lines. The video in a...
CK-12 Foundation
Inscribed Angles in Circles: Lesson
Circle the angles and intercept the arcs. The video introduces three theorems relating to inscribed angles in circles. Using drawings, the segment of a playlist on geometry illustrates the measure of angle along with theorems about two...
CK-12 Foundation
Same Side Interior Angles: Lesson
Supplement your scholars' knowledge of angles involved with parallel lines. Using the properties of alternate interior angles and linear pairs, the presenter shows interior angles located on the same side of a transversal of parallel...
CK-12 Foundation
Alternate Exterior Angles: Lesson
Use an alternate approach to parallel lines. A resource in a comprehensive playlist on basic geometry develops the concept of alternate exterior angles and parallel lines. The presentation demonstrates how to identify alternate exterior...
CK-12 Foundation
Exterior Angles Theorems: Lesson
Use the inside to find the outside. The resource presents two theorems dealing with exterior angles of a triangle. Using the two theorems, the segment from a larger geometry playlist works problems to solve for angle measures.
CK-12 Foundation
Proportions with Angle Bisectors: Lesson
Half at one end becomes proportional on the other. As part of a basic geometry playlist, the video introduces the Angle Bisector Theorem. The presentation uses the theorem to find missing lengths in triangles.
CK-12 Foundation
ASA and AAS Triangle Congruence Lesson
The location of the side makes a difference. One of the videos in a geometry playlist introduces angle-side-angle and angle-angle-side congruence relationships. Using drawings, the video shows how these two congruence statements are...
CK-12 Foundation
Angles Outside a Circle: Lesson
Understand the difference in finding angle measures. A segment of an extensive geometry playlist introduces the formula to find the measure of an angle formed outside of a circle. Using examples, the video shows how to calculate measures...
Socratica
Sum of the Angles in a Triangle
You know that triangles have angle sums of 180 degrees, but can you prove it? A brief video in the Socratica Geometry series highlights an informal geometric proof. It shows that the sum of the interior angles of a triangle is 180...
Corbett Maths
Radius and Tangent – Proof
A tangent line always finds its place at a 90-degree angle to a radius. Many scholars struggle with the proof of the seemingly simple statement. A brief video demonstrates the reasoning behind the proof before pupils practice applying it...
Flipped Math
Unit 1 Review: Tools for Geometry
Pupils review the vocabulary, formulas, and postulates from the opening unit in Geometry. Individuals use these to solve a problem set that requires learners to apply algebraic skills along with providing reasons within a proof. Scholars...
CK-12 Foundation
Triangle Sum Theorem: Lesson
The measures all add up. The presentation, part of a helpful playlist on geometry, provides the statement of the Triangle Sum Theorem. Using the theorem, the video shows how to find the missing measure of an angle.
CK-12 Foundation
SAS Triangle Congruence: Lesson
SAS is not just a spy organization. A section of an extensive geometry playlist introduces a way to show two triangles are congruent, SAS. Using diagrams, the video provides an explanation by showing only one triangle is formed with two...
CK-12 Foundation
SAS Similarity Theorem: Lesson
When given two sides and an angle, make similar triangles. The video describes the SAS Similarity Theorem. Using the theorem, the segment of a larger geometry playlist determines whether two triangles are similar.
Flipped Math
Parallel Lines and Triangles
Triangles bring sums to geometry. The lesson presents two theorems dealing with the angles of a triangle. Pupils learn about the Triangle Sum Theorem and the Exterior Angle Theorem, and then apply the theorems to create equations and...
CK-12 Foundation
Inscribed Quadrilaterals in Circles: Lesson
Find supplementary information about inscribed angles. A section of a large geometry playlist introduces the relationship of angles in an inscribed quadrilateral. The presentation works through examples that use the relationship between...
CK-12 Foundation
Triangle AA Similarity: Lesson
Two sets of congruent angles leads to three. Using diagrams of two triangles, the presentation intuitively shows that if two sets of angles are congruent, the third set is too. The portion of a geometry playlist uses that information to...
CK-12 Foundation
Isosceles Triangles: Lesson
Two sides give us two angles. A segment of a playlist on basic geometry revisits isosceles triangles. The presentation explains several properties and theorems related to isosceles triangles.
CK-12 Foundation
Parallelograms: Lesson
Properties spawn from parallel sides. With the aid of diagrams, the presentation shows the different properties of parallelograms. The segment of an extensive geometry playlist lists the properties that using the parallel sides of a...
Flipped Math
Addition Postulate
Add a little algebra to the geometry. Class members learn about the Addition Postulate for segments and angles. The pupils use their knowledge of solving equations to find lengths of segments and measures of angles. Individuals apply...
Curated OER
How Do You Prove that Two Overlapping Triangles are Congruent?
Given two overlapping triangles with a congruent angle, a common angle, and a congruent side, a simple proof is shown in this video. Using the ASA (angle-side-angle) postulate, the instructor shows how the two triangles are congruent.
CK-12 Foundation
Equilateral Triangles: Lesson
Take a second look at triangles that are equal all the way around. The video reminds viewers what an equilateral triangle is and points out that the three angles are the same. Using the fact that equilateral triangles are also isosceles,...