A circle of constant radius `a` passes through the origin `O` and cuts the axes of coordinates at points `P` and `Q` . Then the equation of the locus of the foot of perpendicular from `O` to `P Q` is `(x^2+y^2)(1/(x^2)+1/(y^2))=4a^2` `(x^2+y^2)^2(1/(x^2)+1/(y^2))=a^2` `(x^2+y^2)^2(1/(x^2)+1/(y^2))=4a^2` `(x^2+y^2)(1/(x^2)+1/(y^2))=a^2`