###
conjecture

an unproven statement that is based on observations

###
point

has no dimension. usually represented by a small dot

###
line

extends in one dimension. usually represented by a straight line with two arrowheads to indicate that the line extends without end in two directions

###
plane

extends in two dimensions. usually represented by a shape that looks like a tabletop or wall

###
line segment

part of a line that consists of two endpoints and all points on the line that are between the endpoints

###
ray

part of a line that consists of an initial point and all points on the line that extend in one direction

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initial point

the starting point of a ray

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postulate

rules that are accepted without proof. also called axioms

###
congruent segments

segments that have the same length

###
congruent angles

angles that have the same measure

###
acute angle

an angle with measure between 0 and 90 degrees

###
obtuse angle

an angle with the measure between 90 and 180 degrees

###
right angle

an angle with measure equal to 90 degrees

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straight angle

an angle with measure equal to 180 degrees

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segment bisector

a segment, ray, line, or plane that intersects a segment at its midpoint

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angle bisector

a ray that divides an angle into two adjacent angles that are congruent

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vertical angles

two angles whose sides form two pairs of opposite rays

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complementary angles

two angles whose measures have the sum of 90 degrees

###
supplementary angles

two angles whose measures have the sum of 180 degrees

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