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### Course: Class 5>Unit 4

Lesson 3: Parallel and perpendicular lines

# Parallel & perpendicular lines

Parallel lines are lines that never intersect, and they form the same angle when they cross another line. Perpendicular lines intersect at a 90-degree angle, forming a square corner. We can identify these lines using angles and symbols in diagrams. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• Are there parallel lines in reality? I mean, each time I draw parallel lines I'm doing my best to make them look like they would never intersect however you extend them on both of their ends, but I think because of many factors when I'm drawing parallel lines (e.g a little shaky hands, bumpy edge of the ruler, soft surface of the paper), the lines aren't really parallel, they will actually intersect at some point when you extend them.
Do machines also have a very slight error when creating parallel lines?
What about computers? Are they really good at processing graphics they are able to create perfectly parallel lines?
Do parallel lines only exist in concept?
• Computers can because they have rows of pixels that are perfectly straight. It's not possible to draw two perfectly parallel lines, just as it isn't possible to draw a perfect circle. So yeah, parallel lines exist, but perfectly replicating them is pretty hard and can't be perfectly recreated by humans.
• Are perpendicular lines intersecting lines,but,intersecting lines not perpendicular lines?
• All perpendicular lines are intersecting lines , but not all intersecting lines are perpendicular lines.
• what are transversals? and how do I use them in Geometry
• Transversals are basically lines intersecting 2 or more lines. There may or may not be employments utilizing this skill, but nevertheless it is very important to learn this while in school (just for the exams at least :)).
• what is that symbol that looks like an upside-down capital T? Does it mean bisects or intercepts or perpendicular?
• The symbol ⊥ is the perpendicular sign - it shows that two lines are perpendicular to each other.

For example:
line AB ⊥ line CD.

Hope this helps!
• Does it have to be a line? Can be line segments or rays?
• Although I'm not exactly sure what you are asking I will explain how Lines, Line Segments, and Rays work. Lines are well lines and do not have any endpoints and are basically infinite. Line segments are like taking a piece of line. They have two endpoints and are not infinite. Last you have the ray which basically is like cutting a line in one spot but leaving one of the sides infinite. One endpoint and is infinite in one direction. Another thing to note is Parallel Lines/Parallel Rays/Parallel Line Segments. Basically they will never touch or get any farther or closer away. If you have other questions feel free to ask them.
• what is the definition of a skew line?
• The definition of a skew line is as follows:
"In three-dimensional geometry, skew lines are two lines that do not intersect and are not parallel." It is important to note the part that says three-dimensional geometry because two lines cannot be skew lines in 2 dimensions. Skew lines are just lines that are in different planes that do not intersect, which fits the definition because two lines being parallel implies they are in the same plane.
• Im having trouble remembering how a line is perpendicular. can someone tell me any tips or tricks for remembering?
• If you are having trouble remembering the difference between parallel and perpendicular lines, remember this: in the word "parallel", the two l's are parallel. Perpendicular lines are the opposite: the l's would make a 't' shape. That might help!
• soo it always at a 90 where it is prependicular? : )
• Actually, yes, lines that are perpendicular will always be at a 90 degree angle where they intersect.