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point

a location in space; it has no size

line

a series of points that extends in opposite directions without end

plane

a flat surface with no thickness. It contains many lines and extends without end in the directions of all its lines

segment

part of a line; it has two endpoints.

ray

part of a line; it has exactly one endpoint. Name its endpoint first

parallel lines

two lines that lie in the same plane and have no points in common

intersecting lines

lines that lie in the same plane and have exactly one point in common

skew lines

lines that lie in different planes; they are not parallel and do not intersect

acute angle

an angle that is less than 90˚

obtuse angle

an angle that is greater than 90˚ and less than 180˚

straight angle

an angle that is equal to 180˚

right angle

an angle that is equal to 90˚

adjacent angles

angles that share a vertex and a side but have no points in their interiors

vertical angles

angles formed by two intersecting lines and are opposite each other. The opposite angles have the same measure

supplementary angles

the sum of the measure of two angles equals 180˚

complementary angles

the sum of the measure of two angles equals 90˚

transversal

a line that intersects two other lines in different points

corresponding angles

angles that lie on the same side of the tranversal and in the same relative position

alternate interior angles

angles between a pair of lines and on the opposite sides of the transversal

vertex

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

perpendicular lines

lines that intersect to form right angles