[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.

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

Discover some theorems about triangles.

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

The Chinese character mark formerly known as "Tan" is the first of two lessons to introduce first grade students to geometry using tangrams. This lesson incorporates history, math, and language arts. In this lesson students will be able...