Circle Terminology
  • Circle A geometric figure composed of points that are equidistant from a given point.
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  • Radius Any segment with endpoints that are the center of the circle and a point on the circle.
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  • Diameter The distance through the circle over the center point.
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  • Chord A segment with endpoints that are on the circle, not passing through the center point.
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  • Secant Any line that intersects a circle in two points.
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  • Interior of a circle Any point on the inside of a circle.
images-1.jpeg(black is the interior of a circle)


  • Exterior of a circle Any points on the outside of a circle.
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  • Central Angle An angle that intersects a circle in two points and has its vertex at the center of the circle.
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  • Arc A part of a circle that is defined by two endpoints.
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  • Minor Arc An arc with a measure less than 180 degrees.
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  • Major Arc An arc with a measure greater than 180 degrees.
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  • Circumscribed A circle around all four vertices of a polygon.
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  • Inscribed A circle on the inside of a square touching each side once.
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  • Pi An irrational number represented by the ratio of the circumference of a circle to the diameter of the circle: Pi= circumference/diameter.
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  • Tangent (Point of Tangency) A line in the plane of a circle that intersects the circle in exactly one point. The point of intersection is called the point of tangency.
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  • Circumference Distance around a circle: Circumference=diameter(pi).
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  • Area Square units of the circle
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  • Central Angle An angle formed by two radii with the vertex being the circle's center.
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