Question

What is the equation of the parabola with a directrix at y = 4 and focus (0, -4)

Answer 1

Just try.....
''The standard form is (x - h)^2 = 4p (y - k), where the focus is (h, k + p) and the directrix is y = k - p.''
Given: focus = (0, -4); directrix is at y=4
h=0

k+p = -4 -(1)
k-p = 4 -(2)
(1) + (2)
2k = 0
k =0
Put k=0 into (1)
0 + p = -4
p =-4

So,

(x - h)^2 = 4p (y - k)
(x-0)^2 = 4 ( -4) (y-0)
x^2 = -16y

I'm not sure if it is correct since I haven't learnt it before.

Answer 2

looks fine to me .... can always use the wolf to dbl chk tho