Geometry Help
Geometry Help: Lines and Angles
Explains the basic concept of lines and angles with step-by-step instructions and methods for solving specific problems on your own relating to this topic.
Dartmouth College
Dartmouth College: The Different Styles of Euclid and Copernicus
A history of the differences between Euclid's and Copernicus's methods of proving geometric ideas.
Maths Challenge
Maths challenge.net: Cables
This is a proof problem, considered a "three star" geometry problem requiring knowledge of proofs and properties of circles to solve this problem with cables in duct problem.
Maths Challenge
Maths challenge.net: Radical Axis
This is a "three star" geometry problem requiring knowledge of proofs and properties of circles. Students will use the given definition of radical axis and prior knowledges to prove a way to find a radical axis.
Varsity Tutors
Varsity Tutors: Hotmath: Algebra Review: Congruent Angles
Find a quick, concise explanation of Congruent Angles. An example is given and clearly explained.
Math Is Fun
Math Is Fun: Triangles Contain 180 Degrees
Students learn about the angle-sum theorem. A definition, example, and proof are included.
Free Math Help
Free Math Help: Angles
The lesson investigates different types of angles used in geometry. Definitions and examples are included.
Shmoop University
Shmoop: Basic Geometry: Angles
The geometry resource explores angles. Descriptions, examples, and practice exercises are included.
Math Is Fun
Math Is Fun: Congruent Angles
Students learn about congruent angles. A definition, example, and tips are included.
Wolfram Research
Wolfram Math World: Postulate
This MathWorld site defines postulates, and explains how and where they are used in mathematics. The site has numerous links to related terms.
Cut the Knot
Cut the Knot!: Proofs in Mathematics
This site provides an explanation of mathematical proofs. It also has links to different types of proofs.
Michigan State University
Michigan State University: Biometrics: Hand Geometry
Students use hand geometry to prove their own identification.
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.