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What's the equation for directrix and focal point of a parabola?

BadAtMath  Sep 22, 2017
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If the parabola is in the from

 

\((x-h)^2=4a(y-k)\)

 

then

The vertex is (h,k)

The focal point is  (h,k+a)      That is a units up from the vertex

and 

The directrix is   y=k-a

Melody  Sep 22, 2017

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