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Mathematics 20 Online
OpenStudy (anonymous):

Find the standard form of the equation of the parabola with a focus at (0, -8) and a directrix at y = 8.

OpenStudy (whpalmer4):

can you tell me which direction this parabola opens?

OpenStudy (anonymous):

uhh it goes down right?

OpenStudy (anonymous):

x = means up, y = means down right? @whpalmer4

OpenStudy (whpalmer4):

if the focus is at (0,-8) and the directrix is at y=8, we have the following picture|dw:1371941924952:dw|

OpenStudy (whpalmer4):

the definition of a parabola is the the set of points equidistant from a point (the focus) and a line (the directrix). where will the vertex of the parabola be in this picture?

OpenStudy (anonymous):

umm... (0, 8)?

OpenStudy (anonymous):

no -8

OpenStudy (anonymous):

0, -8 @whpalmer4

OpenStudy (mertsj):

The vertex is half way between the directrix and the focus.

OpenStudy (anonymous):

so then it's 0,0

OpenStudy (mertsj):

That is correct.

OpenStudy (mertsj):

|dw:1371942449728:dw|

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