We may think of a point as a "dot" on a piece of paper
or the pinpoint on a board. In geometry we usually identify this
point with a number or letter. A point has no length, width, or
height - it just specifies an exact location. It is zero-dimensional.
A line is one-dimensional. That is, a line has length, but no width
or height. In geometry, a line extends forever in both directions. A line is uniquely determined by two points.
The line passing through the
points A and B
is denoted by
The midpoint of a segment divides the segment into two segments
of equal length. The diagram below shows the midpoint M of
the line segment
. Since M is the midpoint, we know that the lengths AM
= MB.
Planes are two-dimensional. A plane has length and width, but no
height, and extends infinitely on all sides. Planes are thought
of as flat surfaces, like a tabletop. A plane is made up of an infinite
amount of lines. Two-dimensional figures are called plane figures.
Space is the set of all points in the three dimensions - length,
width and height. It is made up of an infinite number of planes.
Figures in space are called solids.
Figures in space
Videos
The following video gives the definitions of a point, a line, a plane, and space, as well as the symbols that are used in Geometry to represent each figure.
General Angle Basics: Angle Characteristics - rays, vertex,
Angle Classification - acute angle, right angle, obtuse angle, Complementary and Supplementary Angles
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