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rkahn rkahn
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11 years ago
What is the equation of the parabola, in vertex form, with focus at (2,-4) and directrix y = -6?

(x+2)^2=1/4(y+4)
(x-2)^2=4(y+5)
(x-2)^2=-1/4(y+5)
(y+4)^2=-4(x-2)
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11 years ago
The vertex is midway between the focus and directrix, so it is at (2, -5). That limits your answers to the middle two.

To contain the vertex, the parabola must open upward. That means the answer must be the 2nd one, because opening up means the coefficient in front of (y+5) is positive.

Jen
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