 For a given point "Q"=("a", "b", "c"), the polar conic is the locus of points "P" so that "Q" is on the second polar of "P".In other words, the equation of the polar conic is 
The conic is degenerate if and only if the determinant of the Hessian of "f",
vanishes.Therefore, the equation |"H"("f")|=0 defines a curve, the locus of points whose polar conics are degenerate, of degree 3("n"−"2") called the "Hessian curve" of "C".