###
point

a location in space that has no size

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line

a straight path that extends forever in both directions

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plane

a flat surface that has no thickness and extends forever

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collinear

points that lie on the same straight line

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coplanar

points and lines that lie in the same plane

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line segment

part of a line with two endpoints

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ray

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

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intersection

the place or point where two lines or planes cross each other

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parallel lines

coplanar lines that never intersect

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distance

length of a path between two points

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congruent

figures having the same size and the same shape; equal

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midpoint

the point at which a line segment is divided into two equal segments

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bisect

to divide into two equal parts

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converse

a statement that switches the order of the hypothesis and the conclusion

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conditional statement

an "if-then" statement

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counterexample

an example that proves a statement false

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hypothesis

the "if" part of a conditional statement

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conclusion

the "then" part of a conditional statement

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perpendicular lines

lines that intersect at 90 degree angles

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transitive property

if a=b and b=c, then a=c

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acute triangle

a triangle with all three angles less than 90 degrees

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obtuse triangle

a triangle with one angle greater than 90 degrees

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right triangle

a triangle with one 90 degree angle

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Triangle Sum Theorem

the sum of all three angles in a triangle is 180 degrees

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Exterior Angle Theorem

the measure of an exterior angle of a triangle is equal to the sum of the two remote interior angles of the triangle

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Angle-Side-Angle Congruence

If two angles and the included side of one triangle are congruent to the corresponding two angles and included side of another triangle, then the triangles are congruent.

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Side-Angle-Side Congruence

If two sides and the included angle of one triangle are congruent to the corresponding two sides and included angle of another triangle, then the triangles are congruent.

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Angle-Angle-Side Congruence

If two angles and the non-included side of one triangle are congruent to the corresponding two angles and non-included side of another triangle, then the triangles are congruent.

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Side-Side-Side Congruence

If three sides of one triangle are congruent to three sides of another triangle, then the triangles are congruent.

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Octagon

An eight-sided polygon

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Pentagon

A five-sided polygon

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Triangle

A three-sided polygon

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Hexagon

A six-sided polygon

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Concave

A polygon in which at least one angle curves or dents inward

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Convex

A polygon in which all of the angles curve or bulge outward

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Regular

A polygon with all congruent sides and all congruent angles

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Parallelogram

A quadrilateral with two pairs of parallel sides

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Rhombus

A quadrilateral with four congruent sides

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Square

A quadrilateral with four congruent sides and four right angles

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Trapezoid

A quadrilateral with only one pair of parallel sides

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Translation

A transformation where the pre-image "slides"

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Rotation

A transformation where the pre-image "turns"

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Reflection

A transformation where the pre-image "flips", creating a mirror image

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