Definition and properties of right triangles
Math Open Reference

Great description of the parts of a right triangle
University of Illinois at UrbanaChampaign

A very nice graphical view of the Pythagorean theorem.
math.about

This website will help you with squares and their properties. Such as side length, diagonal length, area and perimeter.
WebMath

This page will allow you to calculate things related to a right triangle. Such as the base, the height, area, perimeter, and Pythagorean Thm.
WebMath

This provides step by step instructions on how to solve for the sides of a right triangle given the area and perimeter.
Analyze Math

A helpful scientific calculator that runs in your web browser window.
Holt Online Learning

Practice using Pythagorean Theorem to solve for the third side of a right triangle. Answers included.
Math.com

All about triangles.
Tim's Triangular Page

A page with links for properties of circles and different types of polygons. Each link has great visuals with clear markings, definitions, and formulas.
Cool Math
