###
line

is perfectly straight and extends forever in both directions

###
plane

is a perfectly flat surface that extends forever in all directions

###
segment

is the part of a line between two points

###
ray

is part of a line that starts at one point and extends forever in one direction

###
angle

is formed by two rays with a common end-point called the vertex.

###
right angle

an angle that measures 90 degrees

###
acute angle

an angle that measures more than zero but less than 90 degrees

###
obtuse angle

an angle that measures more than 90 degrees, but less than 180 degrees

###
complementary angles

two angles whose measures add to 90 degrees

###
supplementary angles

two angles whose measures add up to 180 degrees

###
congruent figures

figures that have the same shape and same size

###
vertical angles

a pair of opposite congruent angles formed by intersecting lines

###
Triangle Sum Theorem

states that the measures of the angles in a triangle add up to 180 degrees

###
acute triangle

has 3 acute angles

###
right triangle

has one right angle

###
obtuse triangle

has one obtuse angle

###
equilateral triangle

has three congruent sides and angles

###
isosceles triangle

has at least two congruent sides and angles

###
scalene triangle

has NO congruent sides or angles

###
polygon

is a closed plane figure formed by three or more sides

###
regular polygon

a polygon with congruent sides and angles

###
trapezoid

a quadrilateral with exactly one pair of parallel sides

###
paralellogram

a quadrilateral that has 2 pairs of parallel sides

###
rectangle

a parallelogram with four right angles

###
rhombus

a parallelogram with all side congruent

###
square

a parallelogram with four right angles and four congruent sides

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