Question 1171333: Given the parabola
(x+2)^2=-8(y-5), which of the following is the vertex and directrix?
The directrix is y=0 and the vertex is (-2,5)
The directrix is y=-4 and the vertex is (-2,5)
The directrix is y=7 and the vertex is (-2,5)
The directrix is y=3 and the vertex is (-2,5)
Found 2 solutions by Edwin McCravy, greenestamps: Answer by Edwin McCravy(20054) (Show Source): Answer by greenestamps(13198) (Show Source):
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The given equation is in vertex form,

where the vertex is (h,k) and p is the directed distance from the directrix to the vertex.
With the given equation, then, you can see immediately that the vertex (h,k) is (-2,5) and 4p=-8 so p is -2.
Since p is the directed distance from the directrix to the vertex, p=-2 means the directrix is 2 units ABOVE the vertex, because it is 2 units down from the directrix to the vertex. So the directrix is at y=5+2=7.
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