Geometry
Terms: Chapter 1
Acute Angle
 An angle with degree measure between
0 and 90.
Adjacent Angles
 Two angles that lie in the same plane,
have a common vertex, and a common
side, but no common interior points.
Angle bisector
 A ray that divides an angle into to
congruent angles
Between/ Betweenness of
points
 For any two points A and B on a line,
there is another point C between A and B
if and only if A, B, and C are collinear
and AC + CB = AB.
Collinear
 Points that lie on the same plane
Complementary Angles
 Two angles with measures that have a
sum of 90.
Concave
 A polygon for which there is a line
containing a side of the polygon that also
contains a point in the interior of the
polygon.
Congruent
 Having the same measure.
Construction
 A method of creating geometric figures
without the benefit of measuring tools.
Generally, only a pencil, straightedge
and compass are used.
Convex
 A polygon for which there is no line that
contains both a side of the polygon and
a point in the interior of the polygon.
Coplanar
 Points that lie in the same plane.
Degree
 A unit of measure used in measuring
angles and arcs. An arc of a circle with a
measure of 1degree is 1/ 360 of the
entire circle.
Exterior
 A point is in the exterior of an angle if it
is neither on the angle nor in the interior
of the angle.
Interior
 A point is in the interior of an angle if it
does not lie on the angle itself and it lies
on a segment with endpoints that are on
the sides of the angle.
Line
 A basic undefined term of geometry. It is
made up of points and has no thickness
or width. In a figure, it is shown with an
arrowhead at each end. Usually named
by lowercase script letters or by writing
the capital letters for two endpoints, with
a double arrow over the pair of letters.
Line Segment
 A measureable part of a line that
consists of two points, called endpoints,
and all of the points between them.
Linear Pair
 A pair of adjacent angles whose non-
common sides are opposite rays.
Locus
 The set of points that satisfy a given
condition.
Midpoint
 The point halfway between the endpoints
of a segment.
N-gon
 A polygon with n sides.
Obtuse Angle
 An angle with degree measure greater
that 90 and less than 180.
Opposite rays
 Two rays BA and BC such that B is
between A and C.
Perimeter
 The sum of the lengths of the sides of a
polygon.
Perpendicular
 Lines that form 4 right angles.
Plane
 A basic undefined term in geometry. It is
a flat surface made up of points that has
no depth and extends indefinitely in all
directions. In a figure, it is often
represented by a shaded, slanted 4sided figure. Usually named by a capital
script letter or by three non collinear
points.
Point
 A basic undefined term in geometry. It is
a location. In a figure, it is usually
represented by a dot and named by a
capital letter.
Polygon
 A closed figure formed by a finite
number of coplanar segments called
sides such that the following conditions
are met:
1. The sides that have a common
endpoint are noncollinear.
2. Each side intersects exactly two other
sides, but only at their endpoints, called
vertices.
Precision
 Depends on the smallest unit available
on the measurement tool.
Ray
 A part of a line. It has one endpoint and
extends indefinitely in one direction.
Regular Polygon
 A convex polygon in which all of the
sides are congruent and all of the angles
are congruent.
Relative Error
 The ratio of the half-unit difference in
precision to the entire measure,
expressed as a percent.
Right Angle
 An angle with a degree measure of 90.
Segment Bisector
 A segment, line, or plane that intersects
a segment at its midpoint.
Sides
 What rays that make up angles are
caled.
Space
 A boundless 3-D set of all points.
Supplementary Angles
 Two angles with measures that have a
sum of 180.
Undefined Terms
 Words, usually readily understood, that
are not formally explained by means of
more basic words and concepts.
Includes: point, line, and plane.
Vertex
 A common endpoint.
Vertical Angles
 Two nonadjacent angles formed by two
intersecting lines.