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# 線、線段與射線 (英): 線、線段與射線之間的差別

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- What I want to do in this video is think about the difference between a line segment (a line segment)
- a line (a line), and a ray (and a ray). And this is kind of the pure geometrical versions of these, of
- these, things. And so a line segment is actually probably what most of us associate with a line in our
- everyday lives. So a line segment is something just like that (for a lack of a better word) a straight
- line, but why we call it a segment is that it actually has a starting and a stopping point. So most of
- the lines we experience in our everyday reality are actually line segments when we think of it from a
- pure geometrical point of view. And i know i drew a little bit of a curve here, but this is supposed
- to be completely straight. But this is a line segment. The segment, the segment is based on the fact
- that it has an ending point and a starting point, or a starting point and an ending point. A line if
- you're thinking about it in the pure geometric sense of a line, is, essentially, it does not stop. It
- doesn't have a starting point and an ending point. It keeps going on forever in both directions so a
- line would look like this (a line, would look like this) and to show that it keeps on going on forever in
- that direction right over there we draw this arrow, and to keep showing that it goes on forever in kind
- of the down left direction, we draw this arrow right over here. So obviously, y-you no I've never encountered
- something that just keeps on going straight forever (forever), but in math (thats the neat thing about math) we
- can think about these abstract notions and so the mathematical purest geometric sense of a line is the
- straight thing that goes on forever. Now a ray is something in between. A ray has a well defined starting
- point (so that's its starting point), but then it just keeps on going on forever. So then, so the ray
- might start over here, but then it just keeps on going (then it just keeps on going). So that right over
- there is a ray. Now that out of the way, let's actually try to do the Khan Academy module on recognizing
- the difference between line segments, lines and rays. And i think you'll find it pretty straight forward
- based on, on our little classification right over here. So let me get the module, let me get the module
- going. (let me, where did i put it? where did i put it? there you go!) Alright, so what is this thing
- right over here? Well it has two arrows on both ends, so it's implying that it goes on forever. So this
- is going to be a line. (lets check our answer.) Yeah! Its a line. (now it's taking some time, oh correct,
- next question) Alright now what about this thing? Wait once again arrows on both sides means that this
- thing is going to go on forever in both directions, so once again it is a line. Fair enough, lets do
- another one. Here, we have one arrow, so it goes on forever in this direction, but it has a well defined
- starting point. So it starts there and then goes on forever. And if you remember that's what a ray is.
- One staring point but goes on forever. So it goes, or more when you think about it, it goes on forever
- in only one direction. So that is a ray. So lets do another question. This right over here, you have
- a starting point and an ending point. Or u can call this the start point and the ending point but it
- doesn't go on forever in either direction. so this right over here, is a line segment. (there you go)
- So hopefully that, that gives you enough t-t-to work your way through this module. And you might notice that
- when i did this (when i did this) module right here, there is no video and that's exactly what this video
- is, it's the video for this module.

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