http://www.ck12.org Chapter 1. Basics of Geometry
Geometry:The study of shapes and their spatial properties.
Building Blocks
Point:An exact location in space.
A point describes a location, but has no size. Dots are used to represent points in pictures and diagrams.
These points are said “PointA,” “PointL”, and “PointF.” Points are labeled with a CAPITAL letter.
Line:Infinitely many points that extend forever in both directions.
A line, like a point, does not take up space. It has direction, location and isalwaysstraight. Lines are one-dimensional
because they only have length (no width). A line can by named or identified using any two points on that line or
with a lower-case, italicized letter.
This line can be labeled
←→
PQ,
←→
QPor justg. You would say “linePQ,” “lineQP,” or “lineg,” respectively. Notice that
the line over the
←→
PQand←→
QPhas arrows over both thePandQ. The order ofPandQdoes not matter.Plane:Infinitely many intersecting lines that extend forever in all directions.
Think of a plane as a huge sheet of paper that goes on forever. Planes are considered to be two-dimensional because
they have a length and a width. A plane can be classified by any three points in the plane.
This plane would be labeled PlaneABCor PlaneM. Again, the order of the letters does not matter. Sometimes,
planes can also be labeled by a capital cursive letter. Typically, the cursive letter written in a corner of the plane.
Example 1:Which term best describes how San Diego, California, would be represented on a globe?
A. point
B. line
C. plane