In this mini-lesson, learn about obtuse triangles including the obtuse triangle definition, sides, properties, examples, and other fun facts related to it.

[Free Registration/Login may be required to access all resource tools.] This study guide reviews terminology for triangles, triangle properties, different types of triangles, and interior and exterior angle theorems.

[Free Registration/Login may be required to access all resource tools.] This study guide reviews the formulas for area and perimeter of triangles and different kinds of quadrilaterals.

Learn about the types of triangles by taking a look at an example and a video lesson.

What better way to get to know your students than with a 1:1 interview. Today you will interview each student on their knowledge of triangles and their ability to separate them from other shapes.

This site from the University of California deals with different applications and topics pertaining to triangles, particularly triangulation.

For this lesson, young scholars learn to classify triangles by the size of the angles and the measures of the sides. Students will use interactives to explore equilateral, isosceles, scalene, acute, obtuse, and right triangles. Included...

Learn about the 30-60-90 triangle with this helpful reference tool. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.

Use your knowledge of 30-60-90 and 45-45-90 triangles to solve some problems.

This tutorial discusses triangle inequality and provides practice problems for students to try out their skills. The teacher resource page contains a lesson plan for a yummy activity involving licorice.

This lesson plan provides students with an opportunity to practice drawing and measuring triangles and angles. It also shows pictures and gives definitions of each type of angle and triangle.

Discover some theorems about triangles.

Explore some problems you can solve with your knowledge of triangles and trigonometry.

Find out about some common centers of triangles.

A complete reference guide to the centroid of a triangle. It provides definitions, examples, and an interactive activity that enhances further explanation. Includes links to related topics.

Learn about the orthocenter of a triangle with this handy reference guide. Provides a detailed definition, examples, and an interactive activity that enhances further explanation. Includes links to related topics.

This site from the University of Saskatchewan provides an explanation of similar triangles, the Pythagorean theorem, and the distance between arbitrary points in a plane. Example problems for each of these concepts are provided.

Find explanations of the ways to prove triangles are congruent. There is a link for Congruence Of Triangles, Part II to find the proofs of some ways to prove congruence of triangles from other postulates (i.e. Assume SAS prove ASA).

In this task, 8th graders investigate congruence and transformations of two triangles on a coordinate grid. Includes a GeoGebra worksheet that the teacher can use for demonstration purposes. Aligns with 8.G.A.2.

Use this applet to show how the placement of the third vertex of a triangle affects the classification of that triangle.

Use this calculator to find the sides, perimeter, area, semiperimeter, and altitude of an isosceles triangle.

Learn how to find the areas and perimeters of triangles and special quadrilaterals.

Plans for building a 3-D triangle with seemingly impossible structure. Good for projects and presentations.

This is the second version of a task asking students to find the areas of triangles that have the same base and height. This presentation is more abstract as students are not using physical models. They still determine the area of each...