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# Rays - Concept

###### Brian McCall

###### Brian McCall

**Univ. of Wisconsin**

J.D. Univ. of Wisconsin Law school

Brian was a geometry teacher through the Teach for America program and started the geometry program at his school

A ray is part of a line, has one fixed endpoint, and extends infinitely along the line from the endpoint. Opposite **math rays** are rays with a common endpoint, extending in opposite directions and forming a line.

If we had a line so it extends infinitely

in either direction, and I picked

an end point somewhere, and I erased everything

that extended beyond that

end point, what I've just

created is a ray.

So a ray has one end point and it extends

infinitely from that end point.

But how do you label a ray?

Well, you start off by saying

what is your end point?

My end point of this ray is A because that's

where it starts, and it extends

through point B. So I'm going to

label this ray A, B as a line but

I only have one arrow.

So the arrow is going

to be over the B.

Because my end point is A and notice I

do not have an arrow over the A, which

tells the geometry student or the geometry

teacher that this ray starts

at A and passes through B.

Now, you can also have opposite rays,

and opposite rays share

a common end point.

So if you look at this line right here,

containing X, Y and Z where X, Y and

Z are all co-linear.

We have opposite rays

if I pick point Y.

So I could say that the ray Y, Z -- so

again I'm saying from point Y through

point Z. So go YZ, and notice how

I level this where the arrow is

over the Z because it starts at Y and

the opposite one would be the ray

starting at Y passing

through X.

So I could label this as ray YX.

So opposite rays share an end point and

rays in general have one end point and

extend infinitely from

that end point.

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###### Brian McCall

B.S. in Chemical Engineering, University of Wisconsin

J.D. University of Wisconsin Law School (magna cum laude)

He doesn't beat around the bush. His straightforward teaching style is effective and his subtle midwestern accent is engaging. There's never a dull moment with him.

##### Concept (1)

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