Definitions worksheet follow-up October 26, 2016

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.

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

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.

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.

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

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.

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?

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.

Other useful vocabulary Adjacent Diagonal