Mentor: Please draw the coordinate axis on your paper. Now label the x and y-axis. Now label each line on the x and y axis with a scale of one.

Mentor: Did you know that the coordinate axis is a plane?

Student: No. What is a plane?

Mentor: A plane is a flat surface that continues out infinitely. The best way to see what a plane is like is to imagine a piece of paper that never ends.

Student: So does infinity mean never ending?

Mentor: Infinity is the biggest number that there is. So a plane stretches out to a point that is so far away we say it never ends.

Student: So a plane stretches out to the end of the universe.

Mentor: Yes, it stretches to the end of the universe and much farther. Now, can any one remember what a line is?

Student: A line is made up of at least two points that are on a straight path.

Mentor: Yes, very good. Let's draw one.

Mentor: Now, does anyone have an idea of what a ray is?

Student: The beam of light that comes out of a ray gun.

Mentor: Good idea. A ray gun has a starting point and it goes on forever if it never hits its target. A ray starts at one point and it continues out to infinity.

Mentor: Let's draw a ray.

Student: So, what is the difference between a line and a ray?

Mentor: A line goes on to infinity in both directions, but a ray stops on one end. If you cut a line in half, you make two rays. Now, can anyone guess what a line segment is?

Student: Is it a line with two ends?

Mentor: Exactly right. A line segment is part of a line that has two endpoints. Let's draw one on paper.

Please direct questions and comments about this project to Addison-Wesley math@aw.com
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