# Figuring out angles between transversal and parallel lines | Geometry | Khan Academy

Let’s say that we have

two parallel lines. So that’s one line

right over there, and then this is

the other line that is parallel to the first one. I’ll draw it as

parallel as I can. So these two lines are parallel. This is the symbol

right over here to show that these two

lines are parallel. And then let me draw

a transversal here. So let me draw a transversal. This is also a line. Now, let’s say that we know

that this angle right over here is 110 degrees. What other angles can

we figure out here? Well, the first thing

that we might realize is that, look, corresponding

angles are equivalent. This angle, the angle

between this parallel line and the transversal,

is going to be the same as the angle

between this parallel line and the transversal. So this right over here is

also going to be 110 degrees. Now, we also know that

vertical angles are equivalent. So if this is 110

degrees, then this angle right over here on the opposite

side of the intersection is also going to be 110 degrees. And we could use that

same logic right over here to say that if this

is 110 degrees, then this is also 110 degrees. We could’ve also

said that, look, this angle right over here

corresponds to this angle right over here so that they

also will have to be the same. Now, what about

these other angles? So this angle right over

here, its outside ray, I guess you could

say, forms a line with this angle right over here. This pink angle is supplementary

to this 110 degree angle. So this pink angle plus 110

is going to be equal to 180. Or we know that this pink angle

is going to be 70 degrees. And then we know that it’s a

vertical angle with this angle right over here, so

this is also 70 degrees. This angle that’s kind of

right below this parallel line with the transversal, the bottom

left, I guess you could say, corresponds to this bottom

left angle right over here. So this is also 70 degrees. And we could’ve also

figured that out by saying, hey, this angle is supplementary

to this angle right over here. And then we could use

multiple arguments. The vertical angle argument,

the supplementary argument two ways, or the corresponding

angle argument to say that, hey, this must be

70 degrees as well.

not gonna say it

love these running throughout my feed 🙂

Thanks, I have a unit assessment on Friday and you made me one review question closer to getting a good grade on it!

Thanks!

whenever i here this guys voice i imagine myself sleeping on a cloud with a boner

im learning this in seventh grade

I am learning a lot

Nice video. Still got a bad grade because I forgot to review the vocabulary. 🙁

But he didn't explain how he got 70 degrees 😕.

Never mind I figured it out😂

these single handedly are getting me through 10th grade geometry

This is very helpful, unless you have a question with decimals and fraction at the same time in it, which is what I have.

Is it bad if I learn this in 7th grade or is this normal

Thanks!

Thanks i understand a lot better

What if it doesn't give you any measures

What app/software are you using to draw these?

Thanks man, this was very helpful. In class I didn't have a clue what was going on my teacher was talking about all sorts of things such as f pattern, c pattern, etc. This is very simple and easy to understand.

Thanks khan for a fabulous lesson! helped me with my studying tonight!

Thanks you so much

my mans doing gods work

yes i get it! thanks

epic!!!! mAATHSS!