###
A plane

Flat surface extending forever in all directions

###
A line

Straight path that extends forever in both directions

###
Line segment

Straight path between two endpoints

###
A angle

A figure formed by two rays that begin at the same point

###
A point

Exact location in space

###
Polygon

Closed figure formed by line segments joined only a their endpoints

###
Parallel lines

Lines that do not cross

###
Perpendicular lines

Lines that cross at 90 degree angle

###
Hexagon

Polygon with six sides

###
Octagon

Polygon with eight sides

###
Decagon

Polygon with ten sides

###
Right angle

Angle that is 90 degrees

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Regular polygon

All sides congruent and all angles congruent

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Diagonal

A line segment that joins two vertices of a polygon but it not a side

###
Obtuse angle

Greater than 90 degrees and less than 180 degrees

###
Acute angle

Angle less than 90 degrees

###
Nonagon

Polygon with nine sides

###
Heptagon

Polygon with seven sides

###
Pentagon

Polygon with five sides

###
Equilateral triangle

Three sides that have the same length

###
Isosceles triangle

Two sides that have the same length

###
Scalene triangle

No sides that have the same length

###
Acute triangle

Less than 90 degrees

###
Right triangle

90 degrees angle

###
Obtuse triangle

Greater than 90 degrees

###
Trapezoid

One pair of opposite sides parallel

###
Parallelogram

Opposite sides parallel, opposite sides congruent

###
Rhombus

Parallelogram, 4 congruent sides

###
Rectangle

Parallelogram, 4 right angles

###
Square

Parallelogram, 4 right angles, 4 congruent sides

###
Transformation

The movement of a geometric figure

###
Intersecting Lines

A straight path that has one end point and extends forever in the opposite direction

###
Congruent figures

Figures that are the same size and same shape

###
Similar figures

Figures that are the same shape and may or may not have the same size

###
Line of symmetry

Place where a figure can be folded so that both halves are congruent

###
Complementary angles

Angles that add up to 90

###
Supplementary angles

Angles that add up to 180

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