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Centroid
The point in a triangle at which the medians of a triangle intersect.
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Circumcenter
The point at which the perpendicular bisectors of a triangle intersect.
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Concurrent
Intersecting at one point; lines, rays, segments, etc. are concurrent when they intersect at one point.
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External Segment
The segment contained by a secant segment with an endpoint on the circle and at the fixed point outside the circle whose points all lie outside the circle (except the endpoint on the circle).
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Incircle
The point in a triangle at which the angle bisectors of a triangle intersect. This point is also the center of a circle inscribed in the triangle.
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Inscribed Angle
An angle whose vertex lies on a circle and whose sides are contained by secant lines.
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Internal Segment
The segment contained by a secant segment whose endpoints are both on the circle.
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Isosceles Trapezoid
A trapezoid with congruent legs.
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Lower Base Angles
The angles in an isosceles trapezoid whose vertices are the endpoints of the longer base.
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Median of a Triangle
A segment within a triangle with one endpoint at a vertex of the triangle and the other endpoint at the midpoint of the side opposite the vertex. Every triangle has three medians.
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Midsegment
A segment within a triangle whose endpoints are midpoints of the sides of the triangle. Every triangle has three midsegments.
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Orthocenter
The point at which the altitudes of a triangle intersect.
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Point of Concurrency
The intersection point of concurrent lines, segments, etc.
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Remote Interior Angles
The two angles of a triangle that are not adjacent to the exterior angle which is drawn by extending one of the sides.
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Secant Segment
A segment with one endpoint on a circle, the other endpoint at a fixed point outside the circle, and one point of intersection with the circle, not including its endpoint.
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Theorem
A statement about geometric figures that has been proved in the past, and can be accepted as a truth in the present without proof. A list of important theorem's can be found in review.
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Upper Base Angles
The two angles of an isosceles trapezoid whose vertices are the endpoints of the smaller base.