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Question 1039378: Identify the equation of the parabola with its focus at (-4,7) and the directrix y=1.
A) 24(y-3)=(x+4)^2
B) 12 (y-4)=(x+4)^2
C) 24 (y-7)=(x+4)^2
D) -12(y+4)=(x+4)^2
Answer by Edwin McCravy(20060)   (Show Source):
You can put this solution on YOUR website!
The equation of a parabola is
4p(y-k) = (x-h)^2
Where
(h,k) is the vertex which is halfway between
the directrix and the focus.
|p| is the distance from the focus to the vertex,
and also from the vertex to the directrix.
p is taken as a positive number if the parabola opens
upward, i.e., the directrix is below the vertex and focus.
p is taken as a negative number if the parabola opens
downward, i.e., the directrix is above the vertex and focus.
You can find those and substitute in
4p(y-k) = (x-h)^2
Edwin
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