National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Standard Form of a Line
Dr. Math gives an inspiring and clear discussion about equations of lines and lines as functions. The Dr. discusses the benefits of the standard form of a line and prompts the student with an equation which can not be written in the...
Sonoma State University
Sonoma State University: Parallel Lines and Similar and Congruent Triangles
This site defines parallel lines, parallel lines cut by a transverse, and congruent triangles. It also contains links for related terms.
Sonoma State University
Sonoma State University: Parallel Lines and Similar and Congruent Triangles
This site defines eleven theorems relating to parallel lines and similar and congruent triangles. Links to the theorems and relevant term descriptions are provided.
Khan Academy
Khan Academy: Angle Relationships With Parallel Lines
Find missing angles given two parallel lines and a transversal.
Varsity Tutors 
Varsity Tutors: Hotmath: Practice Problems: Perpendicular and Parallel Lines
Twenty-two problems present a variety of practice working with perpendicular and parallel lines. They are given with each step to the solution cleverly revealed one at a time. You can work each step of the problem then click the "View...
Wolfram Research
Wolfram Math World: Parallel Lines
A definition for parallel lines in two-dimensional and three-dimensional Euclidean space. The site also gives reference to skew lines and explains the difference between skew and parallel lines in three-dimensional space.
McGraw Hill
Exercises With Parallel Lines and Transversals
This site is a page that students can check their understanding of parallel lines and transversals. The page contains small hints to the solution of each problem, students can check their answers online. After checking their answers they...
The Math League
The Math League: Basic Terms: Parallel Lines
This tutorial provides an explanation and example of parallel lines.
National Council of Teachers of Mathematics
The Math Forum: Parallel Lines and Conic Sections
Dr. Math and a couple of students discuss the possibility of whether parallel lines can be constructed as a degenerate case of conics.
Texas Instruments
Texas Instruments: Parallel Lines
This file contains questions related to parallel lines cut by a transversal and the angles formed. The questions can be used to asses your students' understanding of this topic in geometry.
Shmoop University
Shmoop: Basic Geometry: Parallel Lines & Transversals
The geometry resource explores parallel lines and transversals. Descriptions, examples, and practice exercises are included.
CK-12 Foundation
Ck 12: Algebra: Equations of Parallel Lines
[Free Registration/Login may be required to access all resource tools.] This lesson covers finding the equation of a line that is parallel to a given line.
CK-12 Foundation
Ck 12: Algebra: Determining the Equation of a Line
This comprehensive study guide highlights the main terms and formulas needed to determine the equation of a line. Examples are included.
Texas Education Agency
Texas Gateway: Parallel and Intersecting Lines
This activity provides an opportunity for students to build an understanding of parallel and intersecting lines.
Paul Dawkins
Paul's Online Notes: Algebra: Lines
Detailed math tutorial features notes and examples that discuss graphing lines and introduces the concept of slope, the standard form of the line, the point-slope form, slope-intercept form, and parallel and perpendicular lines.
Cuemath
Cuemath: Lines
Learn all about lines. This lesson targets what is a line and the different types. Check-out the interactive simulations to know more about the lesson and try your hand at solving a few interesting practice questions at the end of the page.
CK-12 Foundation
Ck 12: Geometry: Parallel and Perpendicular Lines
[Free Registration/Login may be required to access all resource tools.] Identifying types of lines as parallel lines, perpendicular lines or intersecting lines.
PBS
Pbs Learning Media: Lines and Angles: Targeted Math Instruction
At the end of this lesson, students will be able to identify and apply the properties of lines and angles and understand the concept of parallel, perpendicular, complementary and supplementary angles, vertical angles, and parallel lines...
Khan Academy
Khan Academy: Identify Parallel and Perpendicular Lines
Recognize parallel and perpendicular lines in geometric figures and pictures. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
CK-12 Foundation
Ck 12: Geometry: Lines and Angles Study Guide
This study guide on lines and angles covers key terminology; line notation; parallel, perpendicular, and skew lines; and postulates and theorems about lines. It is available for download with free registration.
CK-12 Foundation
Ck 12: Algebra: Lines in the Coordinate Plane Study Guide
This comprehensive study guide highlights the main terms and formulas needed to review lines in the coordinate plane. Examples are included.
Texas Instruments
Texas Instruments: Explore Parallel and Perpendicular Lines
Students can use a graphing calculator to explore graphs of parallel and perpendicular lines. Students will find that parallel lines have the same slope and different y-intercepts and that the slopes of two perpendicular lines are...
Texas Instruments
Texas Instruments: Perpendicular or Parallel?
Students can use TI 73 calculators to explore equations that create parallel and perpendicular lines. Teacher will use the screen capture feature of the Navigator system to display students graphs and equations to discuss observations to...
Varsity Tutors 
Varsity Tutors: Hotmath: Graphing Calculator: Parallel, Perpendicular, Slope, Transversal
Practice using your graphing calculator for drawing parallel lines, perpendicular lines, slope, and transversals. If you get stumped or if you would like to check your work, then select the View Solution button, which is located directly...
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