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line

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

ray

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

segment

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

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.

parallel lines

lines in the same plane that never intersect.

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

acute angle

an angle less than 90 degrees but more than 0 degrees

obtuse angle

an angle between 90 and 180 degrees

right angle

an angle that measures 90 degrees

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

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.