Question 932349
Rely on the definition of parabola and use the Distance Formula, unless you already know the formula for a parabola already derived.


The directrix is the general point in your example, of  (-12,y).


{{{sqrt((x-12)^2+(y-0)^2)=sqrt((x-(-12))^2+(y-y)^2)}}}, which should make sense IF you understand the definition of a parabola.  Simplify and put into whichever form you want.