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## 4th grade

### Course: 4th grade > Unit 11

Lesson 3: Parallel and perpendicular# Drawing parallel line segments

CCSS.Math:

Sal draws parallel line segments with given points. Created by Sal Khan.

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- When does a line truly end? When it goes off the paper?(11 votes)
- Lines never end unless they are line segments or rays, which are different from lines. Line segments end from both ends while rays continue from one end forever.(9 votes)

- why does math exist?(12 votes)
- Math is important because it is everything related to counting including time, if math didn't exist we wouldn't be able to tell time, use currency, or even make electronics because all of those things have relation to math. Without math, our species might still be unimportant and not even close to where we are today.(3 votes)

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- I got mine by mastering the exercises. A skill is mastered by earning the crown on top.(5 votes)

- I heard that two parallel lines intercepts itselves in the infinity. Is that true? Why?(3 votes)
- As mentioned by Robin, if they are parallel lines then they would never intercept at any point. They share the same slope or rise/run.(5 votes)

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- i don't get when you say like two endpoints and like zero direction.(4 votes)
- It means that it ends with two points,and zero direction means that it goes for infinity. Right?(4 votes)

- how I can imagine that a line which is not in the axis direction but cover the path of both axes(5 votes)
- I might have missed it in one of the videos, but how do I draw a parallel line using an oblique line and a compass? I didn't understand my teacher when she went over it. Thanks!!(5 votes)
- The whole point is that parallel lines never meet, they are straight and go for infinity(4 votes)

## Video transcript

Any pair of points can be
connected by a line segment. That's right. Connect two pairs
of black points in a way that creates two
parallel line segments. So let's see if we can do that. So I could create
one segment that connects this
point to this point and then another
one that connects this point to this point. And they look pretty parallel. In fact, I think this
is the right answer. If we did it another way, if
we had connected that point to that point and this
point to this point, then it wouldn't
look so parallel. These clearly, if they
were to keep going, they would intersect
at some point. So let me set it back up the
way I did it the first time. Let me make these
two points parallel. And these are line
segments because they have two end points. They each have two end points. And they continue forever. Well they don't
continue forever. They continue forever in no
directions, in zero directions. If it was a ray, it
would continue forever in one direction. If it's a line, it
continues forever past both of these points. In fact, it wouldn't
have end points because it would
just continue forever in both of these directions. Let's do one more. Drag the ray so it
has an endpoint at A, so we want to make its endpoint
at A where the ray terminates and goes through one of
the other black points. The ray should also be
parallel to the pink line. So I have two options. I could make it go
through this black point, but it's clearly not parallel. In fact, it looks
perpendicular here. So let's try to make it
go through this point. Well, yes, when I do that, it
does indeed look like my ray is parallel to the pink line. And this is a ray because
it has one endpoint. This is where the
ray terminates. It's an endpoint. It literally ends there. And it continues forever
in one direction. In this case, the
direction is to the right. It continues forever
to the right. So it continues forever
in one-- continues forever in one direction.