Geometry Definitions

Truth Value: Whether it’s true or false

(Closed) Statement: A sentence that is true or false

Open Statement: The truth value can not be determined

Logically Equivalent: When two statements have the same truth value (three bars)

Some: at least one

Concurrent lines: lines that meet at a single point

Working line: a line you draw to start a construction

Isosceles: triangle with at least 2 congruent sides; legs are always congruent

Equilateral: all sides are equal

Altitude: cevian from vertex and perpendicular to opposite side or extension of the opposite side

Median: cevian from vertex to midpoint of opposite side

Perpendicular Bisector: line perpendicular to a segment through the midpoint of the segment

Angle Bisector: congruent adjacent angles

Linear pair: a set of two adjacent angles whose non-common sides form a straight line. They are supplementary and add up to 180 degrees.

Orthocenter: altitudes (Th 130)

Centroid: medians (Th 131)

Circumcenter: perpendicular bisectors (Th 128)

Incenter: angle bisectors (Th 129)

Circumscribe a circle about a triangle: wrap a triangle with a circle through each vertex

Inscribe a circle in a triangle: fit the largest circle in a triangle where it touches each side once

Auxiliary Lines: a line introduced in a diagram