1. Definitions worksheet follow-up
October 26, 2016

2. Undefined terms Point – has no length or width or depth
Line – has length but no width or depth
Plane – has length and width but not depth
These are all ideal objects
They are also considered to be the basic object of geometry. Everything else can be defined using these three terms.

3. For example
Ray: part of a line that is bounded by a point on one side and unbounded on the other (note that online definitions are not always accurate)
Angle: two rays with a common endpoint

4. Naming conventions Lines:
For lines always use two letters and an arrow above. The order of the letters does not matter.
Rays:
You also use two letters and a directed arrow above. The order of the letters does matter – you have to start with the endpoint.

5. Line segments:
For line segments always use two letters and a line segment above. The order of the letters does not matter – line segments have no orientation
Angles: ABC
The middle letter, B, has to be the vertex of the angle, where the rays BA and BC meet.

6. Skew lines
Where in the classroom can we see two skew lines?

7. Interior angle vs interior of an angle
An interior angle is an angle inside of a polygon
The interior of an angle is the area between the two rays that determine the angle
To further complicate things, there are also alternate interior angles, but we won’t discuss those.

8. What is a right angle? Define a right angle. Define 90 degrees.
Note that you define one in terms of the other. But that is not possible. How else can we define what a right angle is?

9. Polygon definition
A closed plane figure made up of line segments joined end to end without crossing over.
The line segments are called the sides, and the endpoints are called the vertices of the polygon.

10. Other useful vocabulary
Adjacent
Diagonal