Geometry 1.2 - Defined Terms
In lesson 1.1, I talked about terms in geometry that cannot be defined by using simple definitions. In this section, I will discuss geometric terms that can be defined by using terms that have been previously defined (terms and definitions that you learned in algebra) and believe or not, undefined terms will also serve a purpose here. Ready?
Line Segment: A line line segment is part of a line having two points, called endpoints. It also has points between the endpoints. A line segment does not have a set of CONTINUOUS points like a line does. Endpoint means that a line has a beginning and an end. The notation for a line segment in a bar over any letter of choice. Say AB has a bar over it, you would read it as "line segment AB."
Ray: A ray is part of a line having one endpoint and a set of all points on one side of the endpoint. A ray is always named by using two letters of choice. The first letter must be the endpoint. We draw an arrow with an endpoint over the letters.
Angle: An angle is the union of two rays having the same endpoint. The endpoint of an angle is called the vertex; the rays are called the sides of the angle.
There are a few basic ideas in geometry that need to be understood, but are seldom used as reasons in a formal proof.
Here they are:
1-Collinear Points: points that lie on the same line.
2-Coplanar Points: points that lie in the same plane.
3-Opposite rays: 2 rays that lie on the same line, with a common endpoint and no other points in common. Opposite rays form a straight line and/or a straight angle that equals 180º.
4-Parallel lines: two coplanar lines that do not intersect.
By Mr. Feliz
(c) 2007
