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Line Segments

a part of a line; it includes any two points on the line and all the points in between those two points.

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Noncollinear

Not lying on the same line.

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Collinear

Lying on the same line.

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Plane

a flat surface with infinite length and width but no thickness.

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Coplanar

Lying in the same plane.

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Ray

part of a line that begins from an endpoint and extends infitnitely in one direction.

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Postulate

a mathematical statement assumed to be true.

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Theorem

a mathematical statement that has been or is to be proved on the basis of established definitions and properties.

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Proof

a clear, logical structure of reasoning that begins from accepted ideas and proceeds through logic to reach a conclusion.

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Incenter

the center of the circle that can be inscribed within a figure.

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Inscribed Circle

a circle inside a figure and touching exactly one point on each side of the figure.

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Circumcenter

the point at which the perpendicular bisectors of each side of the triangle meet.

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Circumscribed

encircling and touching each vortex of another figure; a circle is circumscribed about a triangle if each vortex of the triangle lies on the circle.

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Median of a Triangle

a straight line that goes through both the vortex and the midpoint of the opposite side, and it divides the triangle into two equal areas.

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Centroid

the point of intersection of the three medians of the triangle.

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