SOLUTION: 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

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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): You can put this solution on YOUR website!
The directrix is y=7 and the vertex is (-2,5)
Answer by greenestamps(13198)   (Show Source): You can put this solution on YOUR website!


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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