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# Parallel & perpendicular lines

Parallel lines are lines in a plane that are always the same distance apart. Parallel lines never intersect. Perpendicular lines are lines that intersect at a right (90 degrees) angle.   Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• 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!
• Couldn't one write that CD is perpendicular to ST and still be correct? This seems a more logical way of stating it, to me.
• Are you referring to what Sal was doing starting at ? You are correct that CD is perpendicular to ST, but at the moment Sal was demonstrating that ST is parallel to UV. He simply used CD as a transversal intersecting these two lines to prove that they are indeed parallel, and in the given illustration CD happened to intersect the lines at a 90 degree angle, making it perpendicular to UV and ST. Fundamentally, you are correct.
• So perpendicular line are 90° angle?
• Well sort of, slightly better wording would be perpendicular lines intersect each other at right (90 degree) angles.
(1 vote)
• 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.
• and they ask us to do it with a set square?? Then how?
• squares have equal amount of there sides. so to do that instaed of adding, multiply.
• What does perpendicular mean?
• line that makes right angle(90 degree) with another line
(1 vote)
• Do you have a easy math?
Because the hard math is a hard one.
Sometimes it gets very, very harder.