###
Point

names a location and has no size

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Line

a straight path that has no thickness and extends forever

###
Plane

a flat surface that has no thickness and extends forever

###
Collinear

points that lie on the same line

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Coplanar

points that lie on the same plane

###
Segment

the part of a line consisting of two points and all the points between them

###
Endpoint

a point at one end of a segment or the starting point of a ray

###
Ray

a part of a line that starts at an endpoint and extends forever in one direction

###
Opposite rays

two rays that have a common endpoint and form a line

###
Postulate (axiom)

a statement that is accepted as true without a proof.

###
Coordinate

a point that corresponds to one and only one number on the ruler

###
Distance

the absolute value of the difference of the coordinates

###
Congruent Segments

segments that have the same length

###
Construction

a way of creating a figure that is more precise

###
Midpoint

the point that bisects, or divides the segment into two congruent segments

###
Segment Bisector

any ray, segment, or line that intersects a segment at its midpoint.

###
Angle

a figure formed by two rays, or sides, with a common endpoint called a vertex

###
Vertex

an angle's common endpoint

###
Interior of an angle

the set off all points between the sides of the angles

###
Exterior of an Angle

the set of all points outside the angle

###
Acute Angle

an angle that measures grater than zero degrees and less than ninety degrees

###
Right angle

an angle that measures ninety degrees

###
Obtuse Angle

an angle that measures grater than ninety degrees and less than one-hundred-eighty degrees

###
Straight Angle

an angle formed by two opposite rays and measures one-hundred-eighty degrees

###
Congruent Angles

angles that have the same measure

###
Angle Bisector

a ray that divides an angle into two congruent angles

###
Adjacent Angles

two angles that are in the same plane with a common vertex and a common side, but no common interior points

###
Linear Pair

a pair of adjacent angles whose non-common sides are opposite rays

###
Complementary Angles

two angles whose measures have a sum of ninety degrees

###
Supplementary Angles

two angles whose measures have a sum of one-hundred-eighty degrees

###
Vertical Angles

two nonadjacent angles formed by two intersecting lines

###
Perimeter

the sum of the side lengths of the figure

###
Area

the number of non-overlapping square units of a given size that exactly covers the figure

###
Base

any side of a triangle

###
Height

a segment from a vertex that forms a right angle with a line containing the base

###
Diameter

a segment that passes through the center of the circle and whose endpoints are on the circle

###
Radius

a segment whose endpoints are the center of the circle and a point on the cicle

###
Circumference

the distance around the circle

###
Pi

ratio of a circle's circumference to its diameter (3.14)

###
Coordinate Plane

a plane that is divided into four regions by a horizontal line

###
Legs

in a right angle triangle, the two sides that form the right angle

###
Hypotenuse

the side across from the right angle that stretches from one leg to the other

###
Transformation

a change in the position, size, or shape, of a figure

###
Preimage

the original figure

###
Image

a figure after transformation

###
Reflection

a transformation across a line. Each point and its image are exactly the same distance from the line

###
Rotation

a transformation about a point. Each point and its image are the same distance from that point

###
Translation

a transformation in which all the points of a figure move the same distance, in the same direction

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