CK-12 Foundation
Ck 12: Elem Math: Classifying Triangles Based on Equal Sides
[Free Registration/Login may be required to access all resource tools.] Students watch a video overview on how to classify triangles based on side length.
CK-12 Foundation
Ck 12: Elem Math: Overview of Rectangles Squares Circles and Triangles
[Free Registration/Login may be required to access all resource tools.] Students watch a video overview on the properties of rectangles, squares, circles and triangles.
CK-12 Foundation
Ck 12: Elem Math: Overview of Special Triangles
[Free Registration/Login may be required to access all resource tools.] Students watch a video overview on how to find missing angles in triangles.
CK-12 Foundation
Ck 12: Elem Math: Overview of Triangle Classifications
[Free Registration/Login may be required to access all resource tools.] Students watch a video overview on how to classify triangles.
Virtual Nerd
Virtual Nerd: What Is the Law of Sines?
The Law of Sines helps with finding a missing side or angle measurement of a triangle. Watch this tutorial to learn about this proportion. [5:57]
Khan Academy
Khan Academy: Triangles: Koch Snowflake Fractal
Explanation of the Koch Snowflake and why it has an infinite perimeter but a finite area.
Khan Academy
Khan Academy: Triangles: Equilateral Triangle Sides and Angles Congruent
A video showing that all of the angles of an equilateral triangle are 60 degrees. The proof is written as a two-column proof.
Khan Academy
Khan Academy: Triangles: Finding Area Using Similarity and Congruence
Explains how to determine the area of a pentagonal shaded region in a triangle. The triangle that is broken into multiple similar and congruent triangles.
Khan Academy
Khan Academy: Triangles: More on Why Ssa Is Not a Postulate
Explains why SSA is not a valid postulate for proving triangle congruence.
Khan Academy
Khan Academy: Worked Examples: Geometry: Geometry: Triangles and Parallelograms
Students explore the properties of triangles and parallelograms in this video tutorial.
Khan Academy
Khan Academy: Triangles: Proving That the Centroid Is 2 3 Rds Along the Median
This video demonstrates that the centroid divides each median into segments with a 2:1 ratio (or that the centroid is 2/3 along the median).
Khan Academy
Khan Academy: Triangles: Triangle Angle Example 3
Explains how to solve for multiple missing angles in a diagram composed of multiple triangles using the triangle sum theorem and other angle relationships.
Khan Academy
Khan Academy: Triangles: 45 45 90 Triangle Side Ratios
Showing the ratios of the sides of a 45-45-90 triangle in this short video.
Khan Academy
Khan Academy: Triangles: Common Orthocenter and Centroid
Showing that a triangle with the same point as the orthocenter and centroid is equilateral in this short video.
Khan Academy
Khan Academy: Triangles: Intro to 30 60 90 Triangles
Explains the special relationship of the lengths of the sides of a 30-60-90 triangle using the Pythagorean theorem.
Khan Academy
Khan Academy: Triangles: Exploring Medial Triangles
This video explains what a medial triangle is and proves that the medial triangle divides the original triangle into four congruent triangles.
Khan Academy
Khan Academy: Triangles: 30 60 90 Triangle Side Ratios Proof
This video explores proving the ratios between the sides of a 30-60-90 triangle.
Khan Academy
Khan Academy: Similarity Example Where Same Side Plays Different Roles
Explains how to determine unknown side lengths in a diagram that involves similar triangles where the two triangles share a side and the shared side corresponds to two different sides in each triangle.
Khan Academy
Khan Academy: Sss to Show a Radius Is Perpendicular to a Chord That It Bisects
More on the difference between a theorem and axiom. Proving a cool result using SSS.
Khan Academy
Khan Academy: Triangles: 45 45 90 Triangles
Students are provided an introduction to 45-45-90 triangles by watching a video tutorial.
Khan Academy
Khan Academy: Triangles: Euler Line
A video demonstration of the magic and mystery of the Euler Line.
Khan Academy
Khan Academy: Worked Examples: Geometry: Pythagorean Theorem, Area
Students watch a video tutorial to learn how to solve area problems of composite figures using the Pythagorean Theorem.
Khan Academy
Khan Academy: Triangles: Area of Koch Snowflake (Part 2) Advanced
In this video students explore summing an infinite geometric series to finally find the finite area of a Koch Snowflake.
Khan Academy
Khan Academy: Triangles: Triangle Area Proofs
A video proving that the area of any triangle is half the product of the base and the height.