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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

initial point

the starting point of a ray

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

straight angle

an angle with measure equal to 180 degrees

segment bisector

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

angle bisector

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

vertical angles

two angles whose sides form two pairs of opposite rays

complementary angles

two angles whose measures have the sum of 90 degrees

supplementary angles

two angles whose measures have the sum of 180 degrees