Locus: When a point moves subject to certain specified conditions, the path traced out by it is called locus.

Equation of a locus: Equation to a locus is the algebraic relation that exists between x and y coordinates of a general point on the locus.

Example:
Find the equation of the locus of points such that the sum of its distances from (0,3) and (0,-3) is 8.


Solution:

(To solve this problem you must know Distance Formula)

Let P(x,y) be any point of the locus and A and B be the points (0,3) and
(0,-3) respectively.