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### Course: Geometry (all content)>Unit 1

Lesson 1: Lines, line segments, and rays

# Identifying rays

A ray is a shape that starts at one point and extends forever in one direction. To identify a ray in a picture, look for a line that has one endpoint (the point where the ray starts) and an arrow on the other end (to show that it keeps going). Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• Can it be FEA?
• No, because if the points were FEA, it would be an angle, specifically an obtuse angle.
• At ; why does a ray need a point on it for it to be a ray? Doesn't it just need an endpoint and then go on forever in one direction?
• I think that if you just had one point then you couldn't know what direction the ray was going. like the sun is the end point but it puts out rays everywhere, so when you have two points you can know in what direction a single ray is going.

This is just how i think of it. I don't know if it'll make sense to anyone else :-/
• Is geometry just reasoning and shapes
• Geometry is the mathematical study of shapes, yes. All math deals with logical reasoning, though it is typically first taught in a formal way in Geometry class.
• isn't the thing in the middle a line? why did he say it was a ray?
• It is a line, but the connected points that make up the line could also result in rays, since a ray only requires a start point and another to specify the direction in which to travel forever. Every combination of points in a line that fulfil these requirements can be used to make a ray.
• So, if more than one ray start at the same point, they are the same ray?

My question being... if there was a question on a test that said:

List all of the rays that can be found on this plane.

Would you just list one for each point? I am a little confused on how to list the rays if some are the same, and if the significance is there.
• They are the same ray if they start on the same point and go the same direction.
• What precisely is the symbol called between the rays CE and CF and the rays FE and FC?
• He is using a slash symbol in a grammatical rather than a mathematical sense, to say that ray CF and ray CE are the same ray. He could have also written an "&" to indicate it.
• can you right a ray like YX but with the arrow pointing <----- instead of XY w/ the arrow pointing ----->
• The arrow over the top is a symbol, and doesn't really indicate which way the ray is headed. This could get tricky if the ray was pointing straight up, or not even in the plane the paper was heading!
You correctly reversed X and Y in your example, to indicate that X was the endpoint, but remember that the first identifier in a ray is supposed to be the endpoint, so it would be improper to write "YX" even though you reversed the ray sign.