Point, line, and plane are the
undefined expression that relinquish the starting location for geometry. When
we define words, we ordinarily use simpler words, and these simpler words are
in turn defined using yet simpler words. This procedure must eventually abort;
at some stage, the definition must use a word whose meaning is accepted as
intuitively clear. Because that meaning is accepted without definition, we
refer to these words as undefined terms. These terms will be used in defining
other terms. Although these expressions are not formally defined, a brief
intuitive dialogue is needed.
A point is the most fundamental
object in geometry. It is represented by a dot and named by a capital letter. A
point constitute position only.
A line (straight line) can be
thought of as a connected set of infinitely many points. It extends infinitely
far in two opposite directions. A line has boundless length, zero width, and
zero height. Any two points on the line name it. The symbol ↔ written on top of
two letters is used to denote that line.
A plane may be contemplating as
an infinite set of points creating a connected flat surface extending
infinitely far in all directions. It is usually represented in drawings by a
four‐sided figure. A single capital letter is used to designate a plane.
