Geometry Definitions

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Points Lines, and Planes

Undefined Terms

Collinear Points

Points that are all in one line

Coplanar Points

Points that are all in one plane

Space

The set of all points

Segment

A part of a line that is bounded by two distinct endpoints.

Ray

A part of a line that is bounded on one side by one distinct endpoint

Angle

A figure formed by two rays pointing away from their point of their intersection

Conditional

An if-then statement representing a hypothesis and a conclusion

Converse

An if-then statement formed by interchanging the order of the hypothesis and the conclusion

Counterexample

An if-then statement determined to have a true hypothesis but a false conclusion

Intersect

To meet or cross paths at a certain point

Midpoint

The middle point of a segment

Bisect

To intersect or split down the middle

Complementary Angles

Two angles whose measures add up to 90

Supplementary Angles

Two angles whose measures add up to 180

Vertical Angles

Two angles formed by intersection whose rays are opposite

Perpendicular Lines

Two lines that intersect to form right angles

Parallel Lines

Coplanar lines that do not intersect

Skew Lines

Noncoplanar lines

Transversal

A line that intersects two or more coplanar lines in different points

Alternate Interior Angles

Two nonadjacent angles on opposite sides of the transversal

Same-Side Interior Angles

Two interior angles on the same side of the transversal

Corresponding Angles

Two angles that share the same positions relative to the two lines