Properties of the Circle
In geometry, a large number of facts about circles and their relations to straight lines, angles and polygons can be proved. These facts are called the properties of the circle.
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Circles having equal radii are congruent.
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Circles having different radii are similar.
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The central angle which intercepts an arc is the double of any inscribed angle that intercepts the same arc (proof).
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The radius perpendicular to a chord bisects the chord.
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The chords equidistant from the center are equal in length.
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A tangent to a circle is at a right angle to the radius at the point of contact.
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Two tangents drawn on a circle from a point outside are equal in length.
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The angle subtended at the center of a circle by its circumference is equal to four right angles.
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The circumference of two different circles is proportional to their corresponding radii.
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Arcs of the same circle are proportional to their corresponding angles.
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Radii of the same circle or equal circles are equal.
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Equal chords have equal circumferences.
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The diameter of a circle is the longest chord.
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Equal circles have equal circumferences.