## Quick Reference

A locus (in the plane) is the set of all points in the plane that satisfy some given condition or property. For example, the locus of all points that are a given distance from a fixed point is a circle; the locus of all points equidistant from two given points, *A* and *B*, is the perpendicular bisector of *AB*. If, in a given coordinate system, a locus can be expressed in the form {(*x*, *y*),| *f*(*x*, *y*)=0}, the equation *f*(*x*, *y*)=0 is called an equation of the locus (in the given coordinate system). The equation may be said to ‘represent’ the locus.

*Subjects:*
Mathematics.

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