Geometry Grades 6-8 by Tiffany Moore and Jenae Hawkins pages 5-14

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opposite rays

Two rays that share an endpoint and extend in opposite directions to form a line

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point

Position in space, often represented by a dot

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ray

A portion of a line that extends from one endpoint infinitely in one direction

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point of intersection

The point at which two lines intersect

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linear

Something that relates to or resembles a line

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midpoint

A point that bisects a line segment

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parallel lines

Lines in the same plane that never intersect

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collinear points

Three or more points that lie in the same line

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perpendicular lines

Two lines that form a right angle at their point of intersection

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line segment

A finite portion of a line that has two endpoints

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line

A set of points in a straight path that extends infinitely in both directions

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plane

A flat surface that extends infinitely in all directions

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coplanar points

Three or more points that lie in the same plane

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flat-plane rule

If three points are coplanar, then the line containing two of the points is in the same plane