Instructional Video
Khan Academy

Khan Academy: Geometry: 30 60 90 Triangles Ii

For Students 9th - 10th
In this video tutorial, the instructor demostrates how to apply the special relationship between the legs and hypotenuse of a 30-60-90 triangle. Solves two different example problems using the relationship. Practice problems available....
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: Challenging Perimeter Problem

For Students 9th - 10th Standards
Demonstrates how to solve a problem from the 2000 American Invitational Mathematics Examination which involves finding the perimeter of a rectangle covered by nine overlapping squares. [9:56]
Instructional Video
Khan Academy

Khan Academy: Geometry: Incenter and Incircles of a Triangle

For Students 9th - 10th Standards
Explains that the intersection of the three angle bisectors of a triangle form the incenter of the triangle. [7:58]
Instructional Video
Khan Academy

Khan Academy: Geometry: Proof Rhombus Area Half Product of Diagonal Length

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

Khan Academy: Geometry: Quadrilateral Properties

For Students 9th - 10th Standards
This video tutorial [5:07] demonstrates how to use the basic properties of parallelograms, rectangles, squares, rhombi, and trapezoids to determine what are the possible ways to name a given geometric shape.
Instructional Video
Khan Academy

Khan Academy: Geometry: Area of Koch Snowflake (Part 1) Advanced

For Students 9th - 10th
Demonstrates how to find the area of a Koch snowflake by summing an infinite geometric series based on the area of an equilateral triangle. [12:30]
Instructional Video
Khan Academy

Khan Academy: Geometry: Challenging Similarity Problem

For Students 9th - 10th Standards
Explains how to determine unknown side lengths in a complex diagram that involves similar triangles. [9:53]
Instructional Video
Khan Academy

Khan Academy: Geometry: Corresponding Angle Equivalence Implies Parallel Lines

For Students 9th - 10th Standards
Proof by contradiction that if two lines cut by a transversal create congruent corresponding angles then the lines are parallel. [5:18]
Instructional Video
Khan Academy

Khan Academy: Geometry: Koch Snowflake Fractal

For Students 9th - 10th
Explanation of the Koch Snowflake and why it has an infinite perimeter but a finite area. [9:11]
Instructional Video
Khan Academy

Khan Academy: Geometry: Equilateral Triangle Sides and Angles Congruent

For Students 9th - 10th Standards
In this video tutorial [6:29], the instructor models a proof so show that if the sides of an equilateral triangle are congruent, then all the angles are congruent and vice versa. The instructor uses the knowledge of congruent legs and...
Instructional Video
Khan Academy

Khan Academy: Geometry: Finding Area Using Similarity and Congruence

For Students 9th - 10th Standards
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. [10:07]
Instructional Video
Khan Academy

Khan Academy: Geometry: Two Column Proof Showing Segments Are Perpendicular

For Students 9th - 10th Standards
In this video tutorial [11:06], the instructor shows how to construct a two-column proof using triangle congruence postulates to prove that two line segments are perpendicular.
Instructional Video
Khan Academy

Khan Academy: Geometry: Proof Rhombus Diagonals Are Perpendicular Bisectors

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 properties of parallelogram diagonals, triangle congruency, and supplementary angles. [4:04]
Instructional Video
Khan Academy

Khan Academy: Geometry: Angle Game (Part 2)

For Students 9th - 10th Standards
Solving for unknown angle measures using knowledge of different angle relationships and the triangle sum theorem. Continuation of Angle Game video. [9:49]
Instructional Video
Khan Academy

Khan Academy: Geometry: The Angle Game

For Students 9th - 10th Standards
Solving for unknown angle measures using knowledge of different angle relationships and the triangle sum theorem. [9:01]
Instructional Video
Khan Academy

Khan Academy: Geometry: 45 45 90 Triangle Side Ratios

For Students 9th - 10th
In this video tutorial [5:42], the instructor explains the ratio of the lengths of the sides in a 45-45-90 triangle using the Pythagorean theorem. Beginning of video concludes a discussion from a previous video on the ratio of the...
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: Intro to 30 60 90 Triangles

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

Khan Academy: Geometry: Similar Example Problems

For Students 9th - 10th Standards
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]
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: 30 60 90 Triangle Side Ratios Proof

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

Khan Academy: Geometry: Similarity Example Where Same Side Plays Different Roles

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

Khan Academy: Geometry:sss to Show a Radius Is Perpendicular to Chord It Bisects

For Students 9th - 10th Standards
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]

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