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Circle- A circle is the set of points in a plane that are equidistant from a given point O. The distance r from the center is called the radius, and the point O is called the center. Twice the radius is known as the diameter d=2r. The angle a circle subtends from its center is a full angle, equal to 360° or radians. The formula for the perimeter of a circle, known as the circumference, is found by the equation: where d=the length of the diameter of the circle. The formula for the Area of a circle is: where r=the length of the radius of the circle. When the coordinates of a circle are centered at the origin the equation for that circle is x² + y² =r².
Ellipse
Parabola
Hyperbola
Inverse Variation
http://mathworld.wolfram.com/Circle.html
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