locusLocus2007-05-22 07:59:402007-05-23 04:18:22Definitioncurvelocusloci% this is the default PlanetMath preamble. as your knowledge
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{\em Locus} (from Latin {\em locus} `\PMlinkescapetext{place, region}') is a set of points satisfying a certain condition and such that no point outside the set satisfies this condition.
For example, in the plane the locus of such point that is at a fixed distance $r$ from a fixed point $O$ is the circle with centre $O$ and radius $r$; the locus of such point which is equidistant from both ends of a line segment is the perpendicular bisector of this line segment.
In general, the loci in the plane are geometric curves; thus one may speak of {\em locus curves}.