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undefined terms

A word that does not have a formal definition, but there is agreement about what the word means. ex: point, line, and plane.

collinear points

Points that lie on the same line.

coplanar points

Points that lie in the same plane.

defined terms

Terms that can be described using known words. ex: line segment and ray.

line segment

Part of a line that consists of two points, called endpoints, and all points on the line that are between the endpoints. Also called segment.

endpoints

The end of a line segment.

ray

Part of a line that consists of a point called an endpoint and all points on the line that extend in one direction.

opposite ray

If point C lies on line "AB" between A and B, the ray "CA" and ray "CB" are opposite rays.

intersection

The set of points that two or more geometric figures have in common.

postulate

A rule that is accepted without proof. Also called axiom

axiom

A rule that is accepted without proof. Also called postulate

coordinate

The real number that corresponds to a point on a line.

distance

Space between two points. Written as AB.

between

When three points lie on a line, you can say that one point is between the other two.

congruent segments

Line segments that have the same length.

midpoint

Point that divides a segment into two congruent segments.

segment bisector

A point, ray, line, segment, or plane that intersects a segment at its midpoint.

angle

Consists of two different rays with the same endpoint. The rays are the sides of the angle, and the endpoint is the vertex of the angle.

acute angle

An angle with measure between 0° and 90°.

right angle

An angle with measure equal to 90°.

obtuse angle

An angle with measure between 90° and 180°.

straight straight

An angle with measure equal to 180°.

congruent angles

Angles that have the same measure.

angle bisector

A ray that divides an angle into two angles that are congruent.

construction

A geometric drawing that uses a limited set of tools, usually a compass and straightedge.

complementary angles

Two angles whose measures have the sum 90°. The sum of the measures of an angle and its complement is 90°.

supplementary angles

The angles whose measures have the sum 180°. The sum of the measures of an angle and its supplement i 180°.

adjacent angles

Two angles that share a common vertex and side, but have no common interior points.

linear pair

Two adjacent angles whose non-common sides are opposite rays.

vertical angles

Two angles whose sides form two pairs of opposite rays.

polygon

A closed plane figure with the following properties. (1) It is formed by three or more line segments called sides. (2) Each side intersects exactly two sides, one at each endpoint, so that no two sides witha common endpoint are collinear.

convex polygon

A polygon such that no line containing a side of the polygon contains a point in the interior of the polygon. A polygon that is not convex is non-convex or concave.

concave polygon

A polygon that is not convex.

n-gon

A polygon with n sides.

equilateral polygon

A polygon with all of its sides congruent.

equiangular polygon

A polygon with all of its interior angles congruent.

regular polygon

A polygon that has all sides and all angles congruent.

Ruler Postulate

The points on a line can be matched one to one with the real numbers. The real number that corresponds to a point is the coordinate of the point. The distance between points A and B, written as AB, is the absolute value of the difference between the coordinates of A and B. (p.9)

Segment Addition Postulate

If B is between A and C, then AB + BC = AC. If AB + BC = AC, then B is between A and C. (p.10)

Protractor Postulate

Consider ray "OB" and a point A on one side of ray "OB". The rays of the form ray "OA" can be matched one to one with the real numbers from 0 to 180. The measure of angle "AOB" is equal to the absolute value of the difference between the real numbers for ray "OA" and ray "OB". (p. 24)

Angle Addition Postulate

If P is in the interior of angle "RST", then the measure of angle "RST" equals the measure of angle "RSP" plus the measure of angle "PST". (p.25)