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: Intro to 30 60 90 Triangles
Solves an example problem in which the length of the hypotenuse is known and the length of a side must be determined. Explains the special relationship of the lengths of the sides of a 30-60-90 triangle using the Pythagorean theorem....
Khan Academy
Khan Academy: Geometry: Similar Example Problems
Explains how to identify and use similar triangles in order to determine unknown side lengths in two given diagrams. Each diagram also applies knowledge of angles formed when parallel lines are cut by a transversal. [7:37]
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: 30 60 90 Triangle Side Ratios Proof
In this video tutorial [6:59], the instructor provides a proof for the relationship among the legs and hypotenuse of 30-60-90 triangles by breaking an equilateral triangle into two congruent triangles and using the Pythagorean threorem.
Khan Academy
Khan Academy: Geometry: 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. [6:05]
Khan Academy
Khan Academy: Geometry:sss to Show a Radius Is Perpendicular to Chord It Bisects
Explains how to prove that a radius is perpendicular to a chord that it bisects by using the side-side-side triangle congruence postulate. [8:19]
Khan Academy
Khan Academy: Geometry: Angle Bisector Theorem Proof
Explanation and proof of angle bisector theorem. [8:35]
Khan Academy
Khan Academy: Geometry: 45 45 90 Triangles
In this video tutorial [9:30], the instructor explains the special relationship of the lengths of the sides of a 45-45-90 triangle. Solves an example problem in which the length of a side is known and the length of the hypotenuse must be...
Khan Academy
Khan Academy: Geometry: Euler Line
Demonstrates that the circumcenter, orthocenter, and centroid of a triangle all lie on a line called an Euler line. [6:12]
Khan Academy
Khan Academy: Geometry: Area of Koch Snowflake (Part 2) Advanced
Explains how to find the area of a Koch snowflake which is represented by an infinite geometric series. Continuation of previous video "Area of Koch Snowflake (part 1) - Advanced" [6:32]
Khan Academy
Khan Academy: Geometry: Triangle Medians and Centroids (2 D Proof)
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...
Khan Academy
Khan Academy: Geometry: Heron's Formula
Demonstrates how to find the area of a triangle using Heron's formula. Practice problems available. [4:43]
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: Area of Diagonal Generated Triangles of Rect. Are Equal
This video tutorial [4:36] shows that the four triangles created by the diagonals of a rectangle all have the same area.
Khan Academy
Khan Academy: Geometry: Pi Is (Still) Wrong
An argument about why tau would be a better, more intuitive circle constant to use instead of pi. [5:17]
Khan Academy
Khan Academy: Geometry: Area and Perimeter
Explains how to calculate the area of rectangles, squares, and triangles, in addition to the perimeter of rectangles and squares. Practice problems available. [12:20]
Khan Academy
Khan Academy: Geometry: Three Points Defining a Circle
Demonstates that any three non-collinear points can be used to define a unique triangle with a unique circumcenter and circumradius. These, in turn, define a unique circle. The center of the circle is the circumcenter of the triangle....
Khan Academy
Khan Academy: Geometry: Figuring Out All Angles for Congruent Triangles Example
Explains how to use given triangle congruency statements to determine the unknown measures of all angles in a diagram where one large triangle is divided into three congruent triangles. [4:35]
Khan Academy
Khan Academy: Geometry: Finding Congruent Triangles
In this video tutorial [7:28], the instructor shows how to determine if two triangles are congruent using different triangle congruence postulates: SSS, SAS, ASA, AAS. Practice problems available.
Khan Academy
Khan Academy: Geometry: 30 60 90 Triangle Example Problem
In this video tutorial [6:40], the instructor explains how to apply the relationships of the sides of a 30-60-90 triangle to solve a perimeter problem involving a rectangle that has had one of the angles trisected.
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: Cylinder Volume and Surface Area
Explains how to calculate surface area and volume of a cylinder. Practice problems available. [8:07]
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