Khan Academy
Khan Academy: Geometry: Triangle Angle Example 1
Explains how to use the triangle sum theorem to solve for missing angle measures in a triangle. Also addresses the relationship between the measure of an exterior angle of a triangle and the measures of the remote interior angles. This...
Planet Nutshell
Planet Nutshell: Math Shorts: Finding Unknown Angles
Planet Nutshell Math Shorts provide animated videos that explain various math topics. On this site students learn about finding unknown angles by using various angle relationships.
Khan Academy
Khan Academy: Doodling in Math: Doodling in Math: Connecting Dots
Anti-parabola propoganda, plus musing on math class, cardioids, connect the dots, envelopes of lines, even a bit of origami.
Khan Academy
Khan Academy: Geometry: Similar Triangles
Explains what it means for two triangles to be similar. Diagram of similar triangles is created with two parallel lines cut by two transversals. [9:34]
Khan Academy
Khan Academy: Geometry: Measuring Angles in Degrees
Explains how to measure an angle in degrees using a protractor. Defines acute, right, and obtuse angles. Practice problems available. [8:22]
Khan Academy
Khan Academy: Geometry: Congruent and Similar Triangles
Explains how to determine if triangles are congruent or similar. [3:53]
Khan Academy
Khan Academy: Geometry: 30 60 90 Triangles Ii
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....
Khan Academy
Khan Academy: Geometry: Rhombus Diagonals
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]
Khan Academy
Khan Academy: Geometry: Challenging Perimeter Problem
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]
Khan Academy
Khan Academy: Geometry: Incenter and Incircles of a Triangle
Explains that the intersection of the three angle bisectors of a triangle form the incenter of the triangle. [7:58]
Khan Academy
Khan Academy: Geometry: Proof Rhombus Area Half Product of Diagonal Length
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]
Khan Academy
Khan Academy: Geometry: Quadrilateral Properties
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.
Khan Academy
Khan Academy: Geometry: Area of Koch Snowflake (Part 1) Advanced
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]
Khan Academy
Khan Academy: Geometry: Challenging Similarity Problem
Explains how to determine unknown side lengths in a complex diagram that involves similar triangles. [9:53]
Khan Academy
Khan Academy: Geometry: Corresponding Angle Equivalence Implies Parallel Lines
Proof by contradiction that if two lines cut by a transversal create congruent corresponding angles then the lines are parallel. [5:18]
Khan Academy
Khan Academy: Geometry: Koch Snowflake Fractal
Explanation of the Koch Snowflake and why it has an infinite perimeter but a finite area. [9:11]
Khan Academy
Khan Academy: Geometry: Equilateral Triangle Sides and Angles Congruent
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...
Khan Academy
Khan Academy: Geometry: 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. [10:07]
Khan Academy
Khan Academy: Geometry: Two Column Proof Showing Segments Are Perpendicular
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.
Khan Academy
Khan Academy: Geometry: Proof Rhombus Diagonals Are Perpendicular Bisectors
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]
Khan Academy
Khan Academy: Geometry: Angle Game (Part 2)
Solving for unknown angle measures using knowledge of different angle relationships and the triangle sum theorem. Continuation of Angle Game video. [9:49]
Khan Academy
Khan Academy: Geometry: The Angle Game
Solving for unknown angle measures using knowledge of different angle relationships and the triangle sum theorem. [9:01]
Khan Academy
Khan Academy: Geometry: 45 45 90 Triangle Side Ratios
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...
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