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Lines, line segments, and rays

Difference between lines, line segments, and rays

Lines, line segments, and rays

Discussion and questions for this video
would an infinite line and an infinite ray be equally long? That's my question.
Yes. It's a tricky concept because it feels like an infinitely long ray is only half as long as an infinitely long line. But technically, half of infinity is still infinity.
What is the difference of a ray line segment and a line?
A line segment connects two points and stops at those two points.
A ray starts at a point and continues forever in one direction.
A line continues forever in both directions.
So then what is the point of infinite ray and infinite line?
A ray begins at a point and then continues on in one direction like the rays of the sun. An infinite line goes off in both directions. It has no beginning and no ending.... much like a highway has many points you can stop along the way but seems to continue on and on in both directions.
A segment(when talking about a line) is only part of a line. Like he said, a line goes on forever but a line segment doesn't. ♥
What if the ray was coming from both sides like this:
Would this be a ray or a line?
what is the difference between a ray segment and a line?
A ray has one endpoint and travels in one direction, while a line is the total opposite of a line segment, having no endpoints and travelling in 2 directions, going into infinity.
at 1:49 in the video, it said that a ray had a well defined starting point? What did they mean? Did they mean the little arrow on the end?
A line is a series of points which keep growing from both ends. A line segment is a portion of line with two end points. A ray is a line which has got one end point. The open end point is infinite.
what are skew lines
In other words, you can only have skew lines in 3 or more dimensions, because in 2D plane geometry, lines are either parallel or intersecting, but not both and not neither.
can a line also be a ray?
Lines cannot be rays.
Line: Extends forever in two directions
Ray: Extends forever in one direction and has one endpoint
Line Segment: Has two endpoints and doesn't extend forever
Rays do relate with line segments. Line segments have at two points in which go on forever in both directions. Rays also have two points, but one point goes forever in a direction and the other point has an endpoint and doesn't extend forever.
if a a ray is infinte but with a starting point does it never come back onto itself? essntialy then turning itself into a line?
Well that cant happen because a ray goes on in one direction for ever, and a line goes on for 2 directions forever.
At 2:33 they say that the figure is a line. But two endpoints are given, so it doesn't make sense for it to be a line and not a line segment.
It's useful to focus on the arrows - at both ends - that tells us, "YES" it can be a line.
(In the video around 1:00 minute, when Sal sketched a line... I think he should sketch two points along the line, however, he was busy emphasizing those arrows at each end to show it is a line.)
It is good that you saw that it seems to represent a line segment, because the two points there, show a segment within the line. (If the question was, can this represent a LINE SEGMENT? it would be right to say, YES.)
A LINE is defined by two points (where any point has a location) and the line does NOT STOP at either point, so two "arrows" in the sketch always means "this is a line."
Two points A and C and the sketch extends with lines and arrows away from both of two points, can correctly be identified as line segment AC, ray AC, ray CA, and line AC (or line CA).
how can you remember the segments more easily
A segment is not infinite and has 2 endpoints.
Is there such thing as a acute line segment
No, "acute" only applies to angles that are smaller than 90 degrees.
What are the similarities and differences between a line and a line segment?
A line segment is a portion of a line that has a finite length.
nowadays why do people call line segments ,lines
In a conversation outside a math classroom, "line" is descriptive enough, But math users like to be precise.
would the steps to finding the answer to these problems, always be the same?
So Is the universe a ray,line or line segment?
The universe is a plane. Like a plane, it goes on forever and ever.
Even though I think I know the answer,why can't an infinite line and an infinite ray be the same?
Does a line have to have arrows at the end?
no:) as long as you don't put endpoints on it, you can leave the sides open.
^see that still counts as a line cause it has no endpoints.
So what is the difference between a ray and a line?
A line goes on forever in both directions. A ray has a starting point, then goes on forever in one direction, kind of like a flashlight beam.
Why would there be line segments inside a line? I thought It was only part of a line and it wouldn't be inside
If there are four points on a line, there are nine different segments. Think of each little space between the points as a segment by itself. All the other segments create other segments, and each single segment can be used as many times as the patterns require. It's the same basic principle as those "Jim has three shirts and three pairs of pants. How many combinations are there?' questions.

Hope this helps and I didn't confuse you!
Sal Just a side note, if you play the video," recognizing lines"in 4th grade, and add captions, it talks about beer and counting Koreans, I think the computer takes what your saying and mishears it.
What If I were to draw a line around the circumference of a sphere for example, the equator. Do I have a line or a line segment?
what's the difference between an infinite ray and a ray?
wouldnt two rays be equally long
what does collinear mean?
Points that lie on the same line are collinear...
•A-------•B-------C• Points A,B,and C are collinear...
would an infinite line and an infinite ray be equally long?
Infinity is infinity. So yes, they would be equally long. Imagine that a ray has a length of infinity. Then imagine a line that has a length of infinity. In theory, they both have lengths of infinity and the line cannot be longer than the ray. Now, if 'infinity' were a normal number, then the line would be twice as long as the ray. But, as I said, infinity is infinity, so in both cases they are extending forever. Hope this helps!
P.S.: This is fun to think about, isn't it?!
What is the difference between a line and line segment? (Curious)
A line goes out to infinity in both directions. A line segment ends and has a finite length.
What happens if you tell the difference?
If a line segment has a starting point and an ending point, and a ray has a starting point but no ending point, and a line has no starting point or ending point, what would you call something with an ending point but no starting point?
The so-called "Ending-point" would be thought of as the starting point. Around 1:40 ish, Sal explains the ray, which your question directly relates to. A ray does have a starting point, but no ending point. Ray = infinite. Good question, though! Hope this helps!
how much time does it take to make one of your supreme videos
If a ray went infinitely around the Earth, would the end of the ray that keeps going meet up with the other end and become a line?
What is described in the question above, is a curve, and it is not in a single direction like a ray has to be in a single direction. A ray can not curve around Earth, a ray can start at Earth and extend to space. Curves, are never rays, or lines, in geometry definitions. A ray can never meet the start point. Also, a line can not be defined as in the question, as something that goes around and meets the starting point, a line can only go infinitely along in directions away from one point, never meeting up "end to end."
Your question is so important because it hints that you are thinking about the idea of a "curved ray" (or "curved line") and you will have a better time with calculus, because you are thinking about "curved lines".
To be certain about solving geometry problems it's important to be certain that a ray is described by an start-point and a single direction, not a curve. A general example is, think of the ray of light (like from a laser) it's got a start point, and goes in a single direction - a ray of light.
(A "curved line" is - mathematically - made of teeny segments connected point to point. Here you are entering into calculus, where the teeny segments get cut up teenier and teenier.)
Hope that helps.
Are lines and rays associated?
why did they come up with signs to represent rays, line segments, and lines?
Can someone make this a little more simple please?
What does congruent mean?
can a ray go on forever
Yes! Actually a ray can go on forever even though it is going in only one direction.
what is the difference between a line segment and a line
A line segment is a segment of a line, also known as a section of a line. They are made up of two points on each end of the segment, with no arrows. A line is a straight mark that consists of two points aswell, but they always have to have the arrows on the ends of the line. A line can go on virtually infinately,since it has those little arrows on the end.
"Coplanar" just means "on the same plane". If you have a bunch of rays and lines, but they're all on the same plane, they're "coplanar".
Is there an easier way to memorize which line, line segment, and ray is which? Like some sort of handy trick...
What is the difference of a ray line segment and a line?
How do u find the ray segment of a line
I'm not sure what your question means. Could you explain further?
Sal mentions the fact that very few objects/situations in our lives go on forever and it got me thinking. Say planet Earth has a single road that goes around the circumference of the planet. Does the road go on forever? I appreciate that if you were to drive on it then it would appear to go on forever but ultimately it's just looping over the same locations.

I guess I'm asking if there is a difference between me shooting a rocket into space that will travel in one direction forever (and constantly going through new space) as oppose to a loop which repeats the same physical space.

Just in case I get attacked by moderators (;-)) my link is to lines and infinity as mentioned in the video.
Wait,so a line is a endless line?
Correct. A line never ends. You might say "but we see lines end all the time when drawing!" well, those are line _segments_ and not lines. In math, they're signified using dots on either side. Lines are represented with arrows pointing outwards in the directions they're going.
what is the difference between a line and a ray?
A line has no endpoints, it goes on forever in two directions.
A ray has one endpoint (which you may think of as its beginning) and then goes on forever in one direction.
A line segment has two endpoints, it does not go on forever at all. Of the three, only the line segment has a finite length.

All three of these, the line, the ray, and the line segment, are perfectly straight without any curving at all.
so how do i know wat the difference is from fay and linesegment
A ray has an arrow on one end and a line stops at two points. The store on the ray represents it going on forever in that direction.

I hope this helps!
can an acute angle go on forever
Yes, because any angle is made up of a series of lines and if you watched this video you know what a line is...so it does go on forever...that is a great question though...
If infinity is forever does that mean half infinity is infinite to
The short answer is no, because infinity isn't really a number
The long answer is in set theory. If you have a set of all the rational numbers (From -infinity through +infinity (Excluding irrationals)) and a set of all the REAL numbers. From (+infinity to -infinity) the two sets are both infinite but different sizes.

As an interesting aside, the set of positive numbers is the same size as the set of negative and positive numbers, which can be shown by a proof that is rather complicated and long to type out here.
Grocery stores go on for EVER for KIDS!
no they don,t grocery stores start at one end and end at another.
that is called a segment line
would an infinite line and an infinite ray be equally long? That's my question.
Yes, a line and a ray are the same length -- both are infinite. I know that common sense would appear to suggest that the line is twice as long, but they are indeed the same length -- the line's infinity is not bigger than the ray's infinity!
Why is a line segment with a ray on one of the points called a ray? Why not call it a line segment?
A line segment has length, which is different from a ray which goes off forever in one direction or a line which goes off forever in both directions.
Where can you find a video about collinear and coplanar lines?
So is a circle a line or a ray?
Neither. Lines and rays are straight, and a circle is not.
What is the difference between rays, lines and line segments?
What is an example of a ray?
A ray is line going off and never stopping like an arrow.
I dont get for the question what is another name for plane R and when ever I try to guess it say im wrong. And I also do not get you video...its a little confussing to me. Is there any way that could help me to understand this?
How come the videos don't work?!
can ray and line be similar?
A ray, and a line, are all about location and about direction; yes, the location and direction of a ray and a line can be related - when we think about geometry and lines and rays we're seeing similarities like how a ray and a line can be described by the same two points, for example.
In my practice questions they keep giving me questions about 'is this colinear' or ' is this coplanar.' There isn't a video about this and i keep getting it wrong. Any help here?
thanks!! I hope i do too
I had an amazing experience watching this video. I watched it twice and learned twice as much than the first time.
At 2:13, a ray is the one with a starting point but going on forever and a line with no starting or ending point - just infinite? I thought it was the other way around.
A ray is the one with a starting point but going on forever and a line with no starting or ending point - just infinite. Those are the correct definitions. Could you reference to where you heard otherwise so I can see?
In this video you explicity state that lines and rays use arrows to denote they continue in both or one direction, respectively. Is this a universal notation used in Geometry? In the exercise following this video, none of the lines or rays have arrows on them and the correct answers do not use the same conventions as demonstrated in this vido.
This video should include what a "line point" specifically is. A line point can be by itself, and doesn't need to be part of a ray, line, or line segment.
is the line segment AB = to AB
Are rays and segments almost the same?
Hmmm..."almost" in definitions is not something mathematicians use...we're kinda anal retentive that way!
BUT, I see where you are coming from. A segment has 2 end points and a finite length. A ray has 1 endpoint and infinite length.
In the quiz he was taking he said the line with a dot and arrow on each side was a line not a line segment. does this mean that even if a line has two dots on it as long as it has two arrows aswell it is classed as a line and not a line segment?
Isnt a line segment just a normal line with a starting and ending point
yes. it was specified in the video
Regarding infinity, how can one even speak of "infinity"? Wouldn't speaking of infinity as an object or something definable necessarily make it finite? I guess another way of putting it is, if infinity cannot be imagined then how can it be made into a meaningful symbol (i.e. there can be no symbol without some "thing" to symbolize)?If it cannot be imagined how can it be spoken of? How can I even make the statement ("infinity cannot be defined") without defining infinity? It's self-contradictory (i.e. I would have to definite infinity to say that it cannot be defined). If infinity can be imagined it would have to have definable boundaries and therefore some "thing" beyond those boundaries which would conflict with the previously defined "infinite-object's" identity as infinite. Am I missing something here or is this just an unsolvable philosophical problem? Or is speaking of infinity as though it were finite just something you have to do for the rest of mathematics to make sense (like trying to imagine a 0-dimensional point)? I'm not sure if this philosophical thinking applies to math in this way so any comments would be appreciated.
why does the line have to be straight
If it isn't straight, it's not a line. A line is the shortest distance between two points.
thanks a lot. but what are points? these always come up in questions and i dont know the answer and mostly fail
A point is an exact position or location on a plane surface. It is important to understand that a point is not a thing, but a place. We indicate the position of a point by placing a dot with a pencil. This dot may have a diameter of, say, 0.2mm, but a point has no size.

I hope this helps :)
I'm still confused on what a plane is?
My computer does not work so well on videos so could i get some short data about how to tell apart a line segment, a ray, and a line?
go into 4 grade math community discusion and there is an answer right above your question.
Can anyone best example representing a ray
you guys should put games on hre educational one after finishing a task
What do you need this for? for any jobs?
I love this video but can a line go and retrace it's steps?
woudnt that be a new line?
So what does collinear, coplaner mean? Isnt there a video for that? i cant find it.
Can someone please help?

~Darshi Ambani
Collinear means on the same line, and coplanar means on the same plane (:
Greetings! I am a 16 year old student who is currently studying algebra 2. Recently, I have been feeling behind and I want to move to studying geometry alongside algebra 2. What would your suggestion be regarding that choice?
Those are online schools or classes?
If a line has three points on it, how many line segments would there be on that line?
Your question does not make sense as phrased. You can make infinitely many line segments from a line. All lines and line segments have infinitely many points.

But, I think what you might have meant was how many line segments can be drawn between 3 collinear points. If that is what you meant, then:
Let A, B, and C be collinear points.
AB is one line segment
AC is a second line segment
BC is a third line segment.
That is all that you can draw.

Remember that line segment AB is the same as line segment BA, as is the case with AC vs. CA and BC vs. CB.
Can line segments be curved?
no, it stays the same.
What is undefinedC? On "measuring segments" it asks this question. The hints do not help. I've tried 40+ answers. Nothing works. I can't find it in the video. Can someone help?
why can't a ray just be a line
Why on a line segment, why are there the two arrows as if it's still calling it a line if the two circles weren't there?
3:30... that took me a while to wrap my head around...
Why are rays lines and line segments called rays lines and line segments?