Question 669617
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Hi,
Standard forms for conics are a 'need to know'
What is the equation of the directrix for the conic section x^2=24y?
the vertex form of a Parabola opening up(a>0) or down(a<0)is {{{y=a(x-h)^2 +k}}} 
where(h,k) is the vertex  and  x = h  is the Line of Symmetry
The standard form is {{{(x -h)^2 = 4p(y -k)}}}, where  the focus is (h,k + p)
and y = -(k+p) is the directrix
x^2=24y, V(0,0), {{{p = 6}}} focus is (0,6) AND DIRECTRIX IS  y = -6
{{{drawing(300,300,   -6, 6, -8, 8,  grid(1),
circle(0, 6,0.3),
circle(0, 0,0.3),
graph( 300, 300, -6, 6, -8, 8,0,-6, x^2/24))}}}