Khan Academy
Khan Academy: Triangles: Similarity Example Problems
Explains how to identify and use similar triangles in order to determine unknown side lengths in two given diagrams.
Virtual Nerd
Virtual Nerd:find the Angles in a Triangle if You Have a Ratio of Their Measures
If you're looking for the measurements of the interior angles of a triangle you can use this tutorial to see how to use a given ratio of the interior angles and the Triangle Sum Theorem to find those missing measurements. [5:39]
Virtual Nerd
Virtual Nerd: Find Missing Angles in an Isosceles Triangle Using Right Triangles
Discover how identifying your triangle first can be very helpful in solving for a missing interior angle measurement. [3:40]
Khan Academy
Khan Academy: Triangles: Similar Triangle Example Problems
Demonstration on how to determine if triangles are similar based on AA, SSS, or SAS similarity postulates.
Imagine Learning Classroom
Learn Zillion: Find Tangent Value Using Side Ratios
In this lesson, you will learn how the ratios of certain sides of the triangle determine the tangent value of a particular angle by using properties of similar triangles. [2:13]
Virtual Nerd
Virtual Nerd: How Do You Find the Sine of an Angle in a Right Triangle?
A trigonometric ratio is a ratio between two sides of a right triangle and includes the sine ratio. Discover how to find the sine of a particular angle in a right triangle by watching this video. [2:48]
Virtual Nerd
Virtual Nerd: How Do You Find the Cosine of an Angle in a Right Triangle?
A trigonometric ratio is a ratio between two sides of a right triangle. The cosine ratio is one of these ratios. Take a look at this tutorial to see how to find the cosine of a particular angle in a right triangle. [3:22]
Khan Academy
Khan Academy: Ca Geometry: More on Congruent and Similar Triangles
Worked examples of similar and congruent triangles.
Khan Academy
Khan Academy: Triangle Similarity & the Trigonometric Ratios
Sal explains how the trigonometric ratios are derived from triangle similarity considerations.
Khan Academy
Khan Academy: Proving Slope Is Constant Using Similarity
Sal uses a clever proof involving similar triangles to show that slope is constant for a line.
Khan Academy
Khan Academy: Geometry Word Problem: A Perfect Pool Shot
Sal uses triangle similarity to plan the perfect shot in a pool game.
Khan Academy
Khan Academy: Challenging Similarity Problem
Interesting similarity problem where we don't have a lot of information to work with.
Sophia Learning
Sophia: Using Right Triangle Trigonometry to Find the Area of Regular Polygons
This lesson will demonstrate how to use right triangle trigonometry and special right triangles (45-45-90 and 30-60-90) to find the area of triangles given the side lengths of the polygon.
Sophia Learning
Sophia: Using Similar Triangles to Make Indirect Measurements
This lesson explains why similar triangles can be used to make indirect measurements, and provides an example.