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Write the equation of a parabola with the focus of (-2,4) and directrix y=2. Show your work including a sketch.

Airey  May 19, 2017
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Since  the vertex is halfway between the focus and the directrix, the vertex must be at (-2,3)

 

So....the distance between the vertex and the focus  =  1  = p

 

So.....using   4py  =  (x - h)^2 + k       where p = 1, h = -2  and k = 3

 

And we have

 

4(1)y  = (x - -2)^2 + 3

 

4y  = ( x + 2) ^2   + 3          multiply both sides by (1/4)

 

y =  (1/4) ( x + 2)^2  + 3

 

Here's the graph : https://www.desmos.com/calculator/dfundaxw40

 

 

cool cool cool

CPhill  May 19, 2017

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