Parabola is defined as the locus of points equidistant from a fixed point (called focus) and a fixed-line (called directrix).
Parabola
Standard Equation of a Parabola For horizontal parabola Let us consider Origin (0,0) as the parabola's vertex A, Two equidistant points S(a,0) as focus, and Z(- a,0) as a directrix point, P(x,y) as the moving point. Let us now draw SZ perpendicular from S to the directrix. Then, SZ will be the axis of the parabola. The centre point of SZ i.e. A will now lie on the locus of P, i.e. AS = AZ. The x-axis will be along the line AS, and the y-axis will be along the perpendicular to AS at A, as in the figure. By definition PM = PS => MP2 = PS2
So, (a + x)2 = (x - a)2 + y2 . Hence, we can get the equation of horizontal parabola as y2 = 4ax . For vertical parabola Let us consider Origin (0,0) as the parabola's vertex A Two equidistant points, S(0,b) as focus and Z(0, -b) as a directrix point P(x,y) as any moving point Let us now draw a perpendicular SZ from S to the directrix. Then SZ will be the axis of the parabola. Now, the midpoint of SZ i.e. A, will lie on P’s locus i.e. AS=AZ. The y-axis will be along the line AS, and the x-axis will be perpendicular to AS at A, as shown in the figure. By definition PM = PS => MP2 = PS2
So, (b + y)2 = (y - b)2 + x2
As a result, the vertical parabola equation is x2 = 4by .