Page 209 - ABCTE Study Guide_Neat

Geometry & Measurement

Two- and Three Dimensional Figures

Lesson Objective

In this lesson you will classify and describe 2- and 3-dimensional figures, and identify parallel and
perpendicular lines. You will use properties of these figures to construct proofs and draw conclusions about
relationships among them.

Geometry: What’s the Point?

The most basic geometric figure is a point. Because it has neither length nor width, it is 0-dimensional. In
fact, every geometric figure is just a collection of points. You may recall that a line segment (usually just
called a “segment”) is the set of all points on a line that lie between two points, called the endpoints. A
collection of points extending forever in one direction from an endpoint is called a ray. Extend it in both
directions and you get a line. A line segment has one dimension, length. Extend the line perpendicular to
its length and you get a 2-dimensional plane. Extend the plane perpendicular to its surface and you get a
3-dimensional space.

In this section we’ll look at two-dimensional figures. These are often called planar figures because they lie
entirely within a plane.

Angles: Defined and Classified

An angle is formed by two rays that share an endpoint. The common endpoint is called the vertex of the
angle. This is B. The interior and exterior of the angle are also labeled.