This lesson focuses on Euclid's Axioms, simple, intuitive statements, that everyone agrees are true. An axiom(or postulate) is a mathematical statement that is regarded as "self-evident" and accepted without proof. A key part of...

This site offers a brief description and an example of a paragraph proof. And remember, "there is never just one way of stating a proof," so others are mentioned as well.

This study guide on parallelograms covers types of quadrilaterals, properties of parallelograms and theorems that describe them, how to identify parallelograms, and special types of parallelograms. It is available for download with free...

Explore and discover the Pythagorean theorem.

Here is a partial list of theorems, postulates, and properties.

This lesson explores triangle inequality theorem, triangle inequality theorem-proof, and triangle inequality theorem problems. Try the hands-on triangle inequality theorem calculator and interactive problems to have a better...

This site from Cut The Knot provides an overview of the law of cosines, complete with an explanation of the law and a proof of the law.

In this lesson, learn all about the 30-60-90 triangle. Learn about its sides, its area, and the rules that apply to these triangles. Includes simulations and practice questions.

This standards-based NCTM website offers resources for teachers of mathematics for all grade levels, including interactive math tools, lesson plans, online resources, and the like.