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### Course: Geometry 227-228>Unit 1

Lesson 1: Angles between intersecting lines

# Angles, parallel lines, & transversals

Parallel lines are lines in the same plane that go in the same direction and never intersect. When a third line, called a transversal, crosses these parallel lines, it creates angles. Some angles are equal, like vertical angles (opposite angles) and corresponding angles (same position at each intersection). Created by Sal Khan.

## Want to join the conversation?

• What does the >> and the > mean?
• They are symbols that tell you these lines are parellel.For example,> is not parellel to >>.
• i couldn't find a video about

-corresponding angles
-alternate exterior angles
-vertical angles
-same-side interior angles
-alternate interior angles
-same side exterior angles

our teacher just threw a bunch of material at us and no one in the class knew what she was talking about. so i came here for help
• These are terms to describe pairs of angles when you have a transversal across two parallel lines.
Draw two parallel lines running horizontally, and draw a non-vertical line across them. You'll get 8 angles. In the upper intersection, starting from the upper-left angle and going clockwise, label the angles A, B, C, D. In the bottom intersection, in the same fashion, label them E, F, G, H.

Then the pairs of corresponding angles are A-E, B-F, C-G, D-H.
The pairs of alternate exterior angles are A-G, B-H.
The pairs of vertical angles are A-C, B-D, E-G, F-H.
The pairs of same-side interior angles are C-F, D-E.
The pairs of alternate interior angles are C-E, D-F.
The pairs of same-side exterior angles are A-H, B-G.
• You said at that there's no proof that corresponding angles are the same. Can't you prove it by making two trapezoids by making a segment perpendicular to the parellel lines on each sides of the transversal?
• I think he means that it's just common sense, but I suppose that could work.
• Why don't we just put two lines between parallel line like this || to signal that they are parallel?
• The mark you have suggested is already being used to show equal line segments (equal in length)
So >> has been used for parallel lines.
• What is the difference between transversal lines and transversal angles? Or are they the same meaning?
• I don't think that there is such thing as transversal angles, only transversal lines. A transversal line is a line that passes through two parallel lines.
• Learnt more from this 7 minute video than I did in a week of school...
• on our goddeses
s
• how do i know if the answer i put is correct
• A great way to know that your answer id correct is by going back and doing a check. Replace the missing value (x) by the answer you got. If you end up with the same answer on both sides, your answer is correct.
• What is the symbol with two vertical lines. Is it a parallel symbol? It looks something like this: ||