### You have heard of points in geometry, or about line segments, or rays; but what tells apart one from the other? What is a plane? Is the plane the figure my teacher draws at the overhead projector? Or is the size of the wall? How should we work with the Segment Addition Postulate? How do I substitute the coordinates in the distance, or in the midpoint formulas? What should be done if I am given an endpoint, and the midpoint to find the other endpoint?

### All these are questions you may be asking yourself. This lesson will enable you to find the answers to them in a very easy, and helpful way. You won't have a teacher rushing you, and you will find that the sequence, and color animations are great clues to follow the flow of the ideas. You will be given problems that you may solve on your own, and they may be solved using the MARKER TOOLS menu using the pen and other tools available there writing directly on the screen. You will love the lesson!

** Lesson's Content **

** Lesson's Glossary **

**Angle **

Geometric shape formed by two rays (initial and ending sides of the angle) that share a common endpoint called the vertex. You may name an angle using the vertex, or a point in each ray and the vertex label in the center.

**Acute angle **

An angle that is between 0 and 90 degrees.

Adjacent angles

If two angles have a common side, a common vertex and no common interior points then they are adjacent.

**Collinear **

In the same line.

**Coplanar **

Within the same plane.

**Line **

An infinite set of points that extends forever in two directions. 2 points on the line allows to uniquely define it.

**Non-Collinear **

Not in the same line.

**Obtuse angle **

An angle whose measure is greater than 90 but less than 180 degrees.

**Plane **

A two-dimensional group of points that goes on infinitely in all directions; made up of infinite lines

**Point **

Indicates a location in space and has no size. It is represented by a dot and usually labeled with uppercase letters. It is uniquely identified by a set of coordinates (x,y) in the plane, and (x,y,z) in the space.

**Ray **

The section of a line that has one endpoint in one side and it never ends at the other side. (flash light beam pointing to the space)

**Segment **

A section of a line, defined by two end points and all the points between them.

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