Learn the four categories of theorems that have to do with lines and angles.

Consider two parallel lines that are intersected by a transversal, and when it crosses the two others, many different angle pairs are formed. See the special properties of the angle pairs in this interactive.

This fourth-grade geometry lesson teaches the definitions for a line, ray, angle, acute angle, right angle, and obtuse angle. We also study how the size of the angle is ONLY determined by how much it has "opened" as compared to the whole...

Construct a copy of a line segment in this interactive exercise.

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

Explore the world of transversals in this mini-lesson. Learn about transversals, transversal lines, and angles. There are transversal examples and a few interesting practice questions at the end of the page to strengthen your concepts of...

Explains the basic concept of perpendicular lines with step-by-step instructions and methods for solving specific problems on your own relating to this topic.

This task uses GeoGebra software, which can be freely downloaded, to explore what happens to the line segments and angles of a triangle when it is reflected, rotated, and translated. Includes printable task sheet for students and a...

This site from Advogato is all about angles. It contains information starting with what an angle is and what it looks like, all the way up to bisecting angles and theorems about angles. This is very good information for students just...

A "convention" is "just the way a thing is done!". This reference material lists some common conventions (notational assumptions) for geometry and trigonometry.

For this task, students are shown a unit circle in a plane and an angle measured from the x-axis. They must determine the coordinates of the line segment for the angle and answer a question about the sum of the coordinates. The purpose...