Geometry: Theorems

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Terms

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Terms

Centroid

The point in a triangle at which the medians of a triangle intersect.
Circumcenter

The point at which the perpendicular bisectors of a triangle intersect.
Concurrent

Intersecting at one point; lines, rays, segments, etc. are concurrent when they intersect at one point.
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).
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.
Inscribed Angle

An angle whose vertex lies on a circle and whose sides are contained by secant lines.
Internal Segment

The segment contained by a secant segment whose endpoints are both on the circle.
Isosceles Trapezoid

A trapezoid with congruent legs.
Lower Base Angles

The angles in an isosceles trapezoid whose vertices are the endpoints of the longer base.
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.
Midsegment

A segment within a triangle whose endpoints are midpoints of the sides of the triangle. Every triangle has three midsegments.
Orthocenter

The point at which the altitudes of a triangle intersect.
Point of Concurrency

The intersection point of concurrent lines, segments, etc.
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.
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.
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.
Upper Base Angles

The two angles of an isosceles trapezoid whose vertices are the endpoints of the smaller base.

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