This site gives a very thorough explanation of how to tell if two triangles are congruent. Dr. Math explains why SSS, SAS, ASA determine that two triangles are congruent. The Dr. gives a few exercises for the reader to try then gives the...

Here is a site that clearly and thoroughly explains how to solve right triangles for any missing side or angle given any two pieces other sides or angles. There are example problems solved, problems for the student to attempt, and...

This study guide on triangle inequalities discusses comparing angles and sides, the Triangle Inequality Theorem, and the Hinge Theorem. It is available for download with free registration.

Learn how similar triangles have congruent corresponding angles and proportional corresponding sides.

This lesson will define the phrase corresponding parts (e.g. angles, sides, etc.). It is 5 of 5 in the series titled "Corresponding Parts."

[Free Registration/Login may be required to access all resource tools.] This lesson introduces the Law of Sines for two cases.

In Spanish. In this interactive activity you can understand and know how to apply direct and inverse homothety to simple shapes, apply Thale's theorem, construct similar polygons and work out their related measurements and know how to...

This task provides a good opportunity to use isosceles triangles and their properties to show an interesting and important result about triangles inscribed in a circle with one side of the triangle a diameter. The fact that these...

In this task, students are asked to draw a quadrilateral so that no two sides are congruent, no two angles are congruent, and no two sides are parallel. The task gives students the opportunity to prove that if we join the midpoints of a...

The goal of this task is to help learners synthesize their knowledge of triangles where only two of the vertices have been given. They will need to know that a triangle inscribed in a circle, with a diameter of the circle as one side, is...

Learn how the Law of Cosines uses the measure of angle C to provide an equation that relates the three sides of the triangle with angle C.

Use this calculator to find the unknown angles in a right triangle using the Pythagorean Theorem. Once you know the sides you can calculate the perimeter, semiperimeter, area, and the altitudes.