City University of New York
Lehman College: An Introduction to Lines
Use this site for two short lesson plans regarding Euclidean and Spherical lines. Intersecting and parallel lines are discussed. The lesson contains activities for two days of class.
CK-12 Foundation
Ck 12: Geometry: Lines in the Coordinate Plane Study Guide
This study guide on lines in a coordinate plane covers key terms, what different line slopes look like, postulates about parallel and perpendicular lines, the slope-intercept equation, how to graph parallel and perpendicular lines, and...
CK-12 Foundation
Ck 12: Interactive Geometry: 4.2 Theorems About 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.
Purple Math
Purplemath: Conventions
A "convention" is "just the way a thing is done!". This reference material lists some common conventions (notational assumptions) for geometry and trigonometry.
Illustrative Mathematics
Illustrative Mathematics: G Gpe, G Co, G Srt Unit Squares and Triangles
In this task, students are shown three unit squares and two line segments connecting two pairs of vertices. They are asked to find the area of a triangle formed by intersecting lines. They can solve it using coordinate geometry or...