Drawing line segments example | Introduction to Euclidean geometry | Geometry | Khan Academy

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.