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point

a location in space that has no size

line

a straight path that extends forever in both directions

plane

a flat surface that has no thickness and extends forever

collinear

points that lie on the same straight line

coplanar

points and lines that lie in the same plane

line segment

part of a line with two endpoints

ray

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

intersection

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

parallel lines

coplanar lines that never intersect

distance

length of a path between two points

infinite

never ending

congruent

figures having the same size and the same shape; equal

midpoint

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

bisect

to divide into two equal parts

converse

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

conditional statement

an "if-then" statement

counterexample

an example that proves a statement false

hypothesis

the "if" part of a conditional statement

conclusion

the "then" part of a conditional statement

perpendicular lines

lines that intersect at 90 degree angles

transitive property

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

acute triangle

a triangle with all three angles less than 90 degrees

obtuse triangle

a triangle with one angle greater than 90 degrees

right triangle

a triangle with one 90 degree angle

Triangle Sum Theorem

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

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

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.

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.

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.

Side-Side-Side Congruence

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

Octagon

An eight-sided polygon

Pentagon

A five-sided polygon

Triangle

A three-sided polygon

Hexagon

A six-sided polygon

Concave

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

Convex

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

Regular

A polygon with all congruent sides and all congruent angles

Parallelogram

A quadrilateral with two pairs of parallel sides

Rhombus

A quadrilateral with four congruent sides

Square

A quadrilateral with four congruent sides and four right angles

Trapezoid

A quadrilateral with only one pair of parallel sides

Translation

A transformation where the pre-image "slides"

Rotation

A transformation where the pre-image "turns"

Reflection

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