Concept:Section of a right circular cone by a plane parallel to a generator of the cone is a parabola.It is a locus of a point, which moves so that distance from a fixed point (FP) (focus) is equal to the distance from a fixed line (directrix)From definition, FP = MP? \(\displaystyle \sqrt{(x-a)^2+(y?0)^2}?=\frac{?x+a??}{1} \)? (x - a)2 + y2 = (x + a)2? y2 = 4axThis is the standard equation of Parabola.Calculation:The focus of the parabola is F (-3,0) and its directrix is the line x = 3 i.e., x - 3 = 0Let P (x,y) be any point in the plane of directrix and focus, and MP be the perpendiculardistance from P to the directrix, then P lies on the parabola if FP = MP?\(\displaystyle \sqrt{(x+3)^2+(y?0)^2}?=\frac{?x-3??}{1} \)Squaring both sides, we get,? x2 + 6x + 9 + y2 = x2 - 6x + 9? 6x + y2 = - 6x? y2 = -12x? y2 = -12x is the required equation of the parabola.