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[[Image:265px-Circle Area svg.png|right|thumb|Area of the circle = '''''π''''' × area of the shaded square]]
[[Image:265px-Circle Area svg.png|right|thumb|Area of the circle = <math>\pi</math> × area of the shaded square]]
A circle is the [[set]] of all the points in a given [[plane]] that are the same distance from a given [[point]] called the center.
A '''circle''' is the [[set]] of all the points in a given [[plane]] that are the same distance, called the [[radius]], ''r'', from a given [[point]] called the center.
A circle may also be defined [[algebra]]ically, as the solutions to an equation of the form:
:<math>x^2 + y^2 = r^2</math>
The measure of the line that forms the circle, or circumference, is given by:
:<math>C = 2\pi*r</math>
The area inside the circle is calculated using the formula:
:<math>A = \pi*r^2</math>
A circle is a [[conic section]], the intersection of a plane with a cone such that the plane is perpendicular to the axis of the cone.
Circles can readily be constructed by using a fixed distance between a pencil point and the center. A [[compass]] is a tool for doing this easily.
A circle with <math>r = 1</math> is called the ''unit circle'', and is used extensively in [[trignometry]].
[[Category:Geometry]]
[[Category:Geometry]]
[[category:mathematics]]