If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Geometry (all content)>Unit 2

Lesson 8: Sal's old angle videos

# Angles of parallel lines 2

Angles of parallel lines examples. Created by Sal Khan.

## Want to join the conversation?

• what are alternate interior, alternate exterior and consecutive angles?
• Since you can't draw with your answer, think about an H with the middle line going out past the two parallel lines. the alternate interior are the angles on opposite sides (such as the top left and the bottom right or the top right and bottom left corners, NOT the top and bottom left or top and bottom right) of the middle line that are inside the two parallel lines. Alternate exterior are just like alternate interior except that they are the angles outside of the two parallel lines. Consecutive angles are the angles that touch each other, the top and bottom corners, and they are inside the parallel lines, although some teachers say they can also be outside the parallel lines.
• Who else agrees that the first problem needs to be corrected ASAP? That is a very obvious mistake when he calls the larger angle 60 degrees, while the angle half its size is 120 degrees! No offense intended, but it needs corrected so no one else is confused by this, agreed?
• Ok. So, the only reason it seems wrong, is because the drawing is not "fit to scale." --> this means that the drawing might not look like he says it is.... Meaning the 60 degrees and the 120 degrees might not look like they "should" be. I do get what you mean though.
• at can you explain what in the world he's talking?
• He's saying that both of those angles are equal to 180 degrees. We already know one of them is 60, so to figure out what the other one is you just subtract 60 from 180. And that will leave you with 120. So that "mystery angle" is 120.
• How come the acute angle is an obtuse angle and the obtuse angle is the acute angle? he made a mistake!
• Never assume that diagrams are drawn to scale. Often test questions will draw the diagram "wrong" on purpose, you can only use the numbers you are given to solve these problems. Don't worry about if it looks right or not.
• Ummm 60 should be the smaller angle since anything under 90 is a acute angle and the other angle is clearly obtuse.
• that is true but ignore that and listen to what he is saying
• what is the sum of interior angles on the same side of transversal between two parallel lines
• Any two angles like that are a value of 180.
• Why did he label the acute angles as 120 degrees and the obtuse angles 60 degrees in the beginning? Shouldn't it be the other way around?
• yes an obtuse angle is and angle over 90 degrees and 60 degrees is an angle under 90 which is called and acute angle.
(1 vote)
• At , isn't an obtuse angle w/ a measure of 60 degrees an impossibility?