Building a Geometry Vocabulary

Select the three undefined terms in geometry.

• point

• angle

• line

• plane

Some beginning principles in geometry are so basic that they cannot be arrived at using simpler facts. A ________ is a statement that is accepted without proof. (E.g. "Exactly one line can be drawn through two points.)

A _______ is a generalization that can be proved to be true. "Prove" simply means presenting a valid argument that uses a set of known facts and logical reasoning to show that a statement is true. (E.g. "The sum of the measures of the three angles of a triangle is 180.")

A ______ indicates position; it has no length, width, or depth. It is named by a single capital letter.

A ____ is a set of continuous points that extends indefinitely in either direction. It is identified by naming two or more points and drawing a line over the letters.

A _____ is a set of points that forms a flat surface that has no depth and that extends indefinitely in all directions; it is usually represented as a closed four-sided figure and is named by placing a capital letter at one of the corners.

A ____ _______ is a part of a line consisting of two points, called endpoints, and the set of all points between them. It is named using the endpoints.

A ___ is a part of a line consisting of a given point, called the endpoint, and the set of all points on one side of the endpoint. It is always named by using two points, the first of which must be the endpoint. The arrow drawn above always points to the right.

_________ rays are rays that have the same endpoint and that form a line.

An _____ is the union of two rays having the same endpoint, called the vertex.