###
line

a series of points that extend in opposite directions without end.

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ray

a part of a line with one endpoint and all points of the line on one side of the endpoint.

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segment

a part of a line with two endpoints and all points in between.

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plane

a flat surface that extends indefinitely in all directions and has no thickness.

###
intersecting lines

lie in the same plane and have exactly one point in common.

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parallel lines

lines in the same plane that never intersect.

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skew lines

lie in different planes and are neither parallel nor intersecting.

###
angle

is a figure formed by two rays with a common endpoint.

###
vertex

the point of intersection of two sides of an angle or figure.

###
point

a location in space that has no size

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acute angle

an angle less than 90 degrees but more than 0 degrees

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obtuse angle

an angle between 90 and 180 degrees

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right angle

an angle that measures 90 degrees

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straight angle

an angle of 180 degrees

###
complementary angles

Two angles whose sum is 90 degrees

###
supplementary angles

Two angles whose sum is 180 degrees

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adjacent angles

are a pair of angles with a common vertex and a common side, but no common interior points

###
vertical angles

opposite angles formed by two intersecting lines

###
congruent angles

angles that have equal measures

###
congruent sides

sides that have the same length.

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