Other
Georgia Tech: The Four Color Theorem
An explanation and proof of the Four Color Map Theorem. Includes illustrative images and a plethora of information.
Paul Dawkins
Paul's Online Notes: Calculus I: Proof of Trig Limits
The tutorial investigates the squeeze theorem. Class notes, definitions, and examples with detailed solutions are included. The class notes are available in pdf format.
Cut the Knot
Cut the Knot!: Analogues and Generalization of the Pythagorean Theorem
This site discusses the theorems and other findings which are directly related to the fundamental Pythagorean theorem. Be sure to click on the link to information on Pythagorean theorem to find several proofs of the theorem.
University of British Columbia
University of British Columbia: Proof of the Pythagorean Theorem
A geometric model that proves the Pythagorean Theorem in a step-by-step diagram that students can advance at their own pace. Requires Java.
Alabama Learning Exchange
Alex: The Pythagorean Theorem in the Real World
The introduction of this lesson has students verifying the famous Pythagorean Theorem with a hands-on proof. Students will then apply the Theorem in one of two ways: by solving for the side lengths of a right triangle and by determining...
Mathematics Archives
Math Archives: Visual Calculus: Antiderivatives/average Value of a Function
This site has the definition of average of a function by using integrals. The site also contains the proof of the mean value theorem which may be viewed one step at a time. There are links to related exercises whose answer is shown one...
Stanford University
Stanford Encyclopedia of Philosophy: Frege's Logic
Lengthy and detailed, but also quite technical, article explaining the major theorems of Frege's logic. Introduction gives a helpful overview and bibliography is included at end, but anyone without a background in logical notation may...
Other
Platonic Realms: Conic Sections
A proof to show that the square root of two is an irrational number, followed by a shorter and even more beautiful proof.
PBS
Using the Pythagorean Puzzle
A printable expercise for students to find that the Pythagorean Theorem works. There are links to problems solving problems using the formula.
Varsity Tutors
Varsity Tutors: Hotmath: Algebra Review: Angle Sum Theorem
Find a quick, concise explanation of the Angle Sum Theorem. A step by step explanation of the proof is included to help you understand the theorem.
Cut the Knot
Cut the Knot!: Napoleon's Theorem
This site gives an explanation of Napolean's Theorem and gives several links to Napoleon's Theorem.
Oswego City School District
Regents Exam Prep Center: Triangle Inequality Theorems
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.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: De Moivre's Theorem Proof
This Math Forum site contains a brief proof of De Moivre's Theorem ((cos(x)+isin(x))^n = cos(nx) + isin(nx)) Where n is an integer.
Other
Mathematical the Four Color Theorem and Computer Proof
This site describes the role of computer involvement in the four color map theorem.
Khan Academy
Khan Academy: Inscribed Angle Theorem Proof
Proving that an inscribed angle is half of a central angle that subtends the same arc.
Shodor Education Foundation
Shodor Interactivate: Squaring the Triangle
Learn about how the Pythagorean Theorem works through investigating the standard geometric proof.
Cut the Knot
Cut the Knot!: Monge's Theorem of Three Circles and Common Tangents
Very good site presenting a Trig problem dealing with tangents lines and circles, then linking the student to the solution
Wolfram Research
Wolfram Math World: Two Column Proof
MathWorld gives a discussion of the use of two-column proofs by high school and middle school students and its relevance to mathematicians.
Mathematics Archives
Math Archives: Visual Calculus: Quotient Rule
This site gives the quotient theorem and examples that the student can work through.
CK-12 Foundation
Ck 12: Geometry: Parallelograms Study Guide
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...
Cut the Knot
Cut the Knot!: The Law of Cosines (Cosine Rule)
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.
Other
Antonio Gutierrez: Geometry From the Land of the Incas
Discovering the properties of constructions, seeing proofs in action, and viewing problems come to life here with this wonderful use of technology in the classroom. Single steps are explained and illustrated one at a time so that the...
TED Talks
Ted: Ted Ed: How to Prove a Mathematical Theory
Explore mathematical proofs and how they are used in our everyday life with this animated video. [4:39]
Mathigon
Mathigon: Graphs and Networks: Map Colouring
This lesson focuses on map coloring and the problem of proving that 4 colors would work for all maps. Francis Guthrie had to color a map of counties in England. He observed that four colors seemed to suffice for any map he tried, but he...