Cool Math
Coolmath: Parallel Lines
This CoolMath resource will help students understand how to use slope and the point-slope form to determine if two lines are parallel.
Math Open Reference
Math Open Reference: Perpendicular Lines
A complete reference guide to perpendicular lines. It provides definitions, examples, and an interactive activity that enhances further explanation. Includes links to related topics.
Cuemath
Cuemath: Perpendicular Bisectors
Provides a definition and examples of perpendicular bisectors.
Khan Academy
Khan Academy: Parallel & Perpendicular Lines From Equation
Use your knowledge about the slopes of parallel and perpendicular lines to solve some problems. For example, what's the equation of the lineperpendicular to y=3x-3 and passes through the point (-8, -2).
Khan Academy
Khan Academy: Parallel & Perpendicular Lines From Graph
Given points that two lines go through or the graph of each line, classify the lines as parallel, perpendicular, or neither.
CK-12 Foundation
Ck 12: Interactive Geometry: 10.4 Slope of Parallel and Perpendicular Lines
Understand how to find the slope of parallel and perpendicular lines.
CK-12 Foundation
Ck 12: Interactive Geometry: 5.3 Parallel and Perpendicular Line Constructions
Understand the step-by-step processes used to create accurate geometric figures.
Geometry Help
Geometry Help: What Are Perpendicular Lines in Geometry?
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.
Wolfram Research
Wolfram Math World: Perpendicular Lines
This site explains what perpendicular means geometricly in mathematics, gives reference to orthoginality, and explains notation for perpendicular segments or lines.
ClassFlow
Class Flow: Parallel and Perpendicular Lines
[Free Registration/Login Required] This flipchart defines and gives opportunities to work with parallel and perpendicular lines. Prentice-Hall, bsee, Parallel, Perpendicular, 5.8, Algebra.
Free Math Help
Free Math Help: Parallel Lines
The Geometry session explores parallel lines. Properties, definitions, and examples are included.
Varsity Tutors
Varsity Tutors: Hotmath: Slope of a Line
Twenty-two problems present a practice finding the slope of a line. The solutions are only available with a paid subscription.
ClassFlow
Class Flow: Parallel Lines and Planes
[Free Registration/Login Required] This flipchart defines parallel lines and planes. It defines a transversal, the concept of alternate angles, and vertical angles.
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.
Varsity Tutors
Varsity Tutors: Hotmath: Algebra Review: Perpendicular and Parallel Lines
Find a quick, concise explanation of what perpendicular lines are. An example is given and clearly explained. Also, parallel lines are explained.
University of Georgia
University of Georgia: Inter Math: Perpendicular Lines
This site from InterMath opens with a very simple definition of perpendicular lines and has links to challenging problems, more information, related terms and everyday examples of perpendicular lines.
National Council of Teachers of Mathematics
The Math Forum: Math to Build On: Crossing & Parallel Lines
A definition of parallel lines that draws a comparison to planes and provides drawings for examples.