# Conchoid

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of a curve

The planar curve obtained by increasing or decreasing the position vector of each point of a given planar curve by a segment of constant length . If the equation of the given curve is in polar coordinates, then the equation of its conchoid has the form: . Examples: the conchoid of a straight line is called the Nicomedes conchoid; the conchoid of a circle is called the Pascal limaçon.