0:00:00.770,0:00:04.070
Any pair of points can be[br]connected by a line segment.

0:00:04.070,0:00:05.150
That's right.

0:00:05.150,0:00:07.350
Connect two pairs[br]of black points

0:00:07.350,0:00:10.939
in a way that creates two[br]parallel line segments.

0:00:10.939,0:00:12.230
So let's see if we can do that.

0:00:12.230,0:00:13.646
So I could create[br]one segment that

0:00:13.646,0:00:16.264
connects this[br]point to this point

0:00:16.264,0:00:17.680
and then another[br]one that connects

0:00:17.680,0:00:20.640
this point to this point.

0:00:20.640,0:00:22.170
And they look pretty parallel.

0:00:22.170,0:00:23.920
In fact, I think this[br]is the right answer.

0:00:23.920,0:00:26.253
If we did it another way, if[br]we had connected that point

0:00:26.253,0:00:30.530
to that point and this[br]point to this point,

0:00:30.530,0:00:32.590
then it wouldn't[br]look so parallel.

0:00:32.590,0:00:35.822
These clearly, if they[br]were to keep going,

0:00:35.822,0:00:37.280
they would intersect[br]at some point.

0:00:37.280,0:00:39.930
So let me set it back up the[br]way I did it the first time.

0:00:39.930,0:00:44.710
Let me make these[br]two points parallel.

0:00:44.710,0:00:46.640
And these are line[br]segments because they

0:00:46.640,0:00:48.340
have two end points.

0:00:48.340,0:00:50.490
They each have two end points.

0:00:50.490,0:00:51.810
And they continue forever.

0:00:51.810,0:00:53.185
Well they don't[br]continue forever.

0:00:53.185,0:00:56.820
They continue forever in no[br]directions, in zero directions.

0:00:56.820,0:00:59.042
If it was a ray, it[br]would continue forever

0:00:59.042,0:00:59.750
in one direction.

0:00:59.750,0:01:01.860
If it's a line, it[br]continues forever

0:01:01.860,0:01:03.130
past both of these points.

0:01:03.130,0:01:04.629
In fact, it wouldn't[br]have end points

0:01:04.629,0:01:06.310
because it would[br]just continue forever

0:01:06.310,0:01:10.060
in both of these directions.

0:01:10.060,0:01:12.510
Let's do one more.

0:01:12.510,0:01:15.610
Drag the ray so it[br]has an endpoint at A,

0:01:15.610,0:01:18.570
so we want to make its endpoint[br]at A where the ray terminates

0:01:18.570,0:01:20.740
and goes through one of[br]the other black points.

0:01:20.740,0:01:23.304
The ray should also be[br]parallel to the pink line.

0:01:23.304,0:01:24.220
So I have two options.

0:01:24.220,0:01:25.790
I could make it go[br]through this black point,

0:01:25.790,0:01:27.190
but it's clearly not parallel.

0:01:27.190,0:01:29.394
In fact, it looks[br]perpendicular here.

0:01:29.394,0:01:31.310
So let's try to make it[br]go through this point.

0:01:31.310,0:01:34.840
Well, yes, when I do that, it[br]does indeed look like my ray

0:01:34.840,0:01:37.290
is parallel to the pink line.

0:01:37.290,0:01:39.320
And this is a ray because[br]it has one endpoint.

0:01:39.320,0:01:40.695
This is where the[br]ray terminates.

0:01:40.695,0:01:41.910
It's an endpoint.

0:01:41.910,0:01:43.580
It literally ends there.

0:01:43.580,0:01:45.717
And it continues forever[br]in one direction.

0:01:45.717,0:01:47.550
In this case, the[br]direction is to the right.

0:01:47.550,0:01:48.966
It continues forever[br]to the right.

0:01:48.966,0:01:52.300
So it continues forever[br]in one-- continues forever

0:01:52.300,0:01:54.710
in one direction.