WEBVTT

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Any pair of points can be
connected by a line segment.

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That's right.

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Connect two pairs
of black points

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in a way that creates two
parallel line segments.

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So let's see if we can do that.

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So I could create
one segment that

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connects this
point to this point

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and then another
one that connects

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this point to this point.

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And they look pretty parallel.

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In fact, I think this
is the right answer.

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If we did it another way, if
we had connected that point

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to that point and this
point to this point,

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then it wouldn't
look so parallel.

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These clearly, if they
were to keep going,

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they would intersect
at some point.

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So let me set it back up the
way I did it the first time.

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Let me make these
two points parallel.

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And these are line
segments because they

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have two end points.

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They each have two end points.

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And they continue forever.

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Well they don't
continue forever.

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They continue forever in no
directions, in zero directions.

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If it was a ray, it
would continue forever

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in one direction.

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If it's a line, it
continues forever

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past both of these points.

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In fact, it wouldn't
have end points

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because it would
just continue forever

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in both of these directions.

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Let's do one more.

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Drag the ray so it
has an endpoint at A,

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so we want to make its endpoint
at A where the ray terminates

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and goes through one of
the other black points.

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The ray should also be
parallel to the pink line.

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So I have two options.

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I could make it go
through this black point,

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but it's clearly not parallel.

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In fact, it looks
perpendicular here.

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So let's try to make it
go through this point.

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Well, yes, when I do that, it
does indeed look like my ray

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is parallel to the pink line.

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And this is a ray because
it has one endpoint.

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This is where the
ray terminates.

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It's an endpoint.

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It literally ends there.

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And it continues forever
in one direction.

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In this case, the
direction is to the right.

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It continues forever
to the right.

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So it continues forever
in one-- continues forever

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in one direction.