how do you know the direction of a parabola?

G

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How do you know which way a parabola is facing when only given the focus and the directrix

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If the directrix is horizontal then the parabola opens up or down.
If the directrix is vertical then the parabola opens right or left.
If the directrix is horizontal and the focus is above then the parabola opens up.
If the directrix is horizontal and the focus is below then the parabola opens down.
Similar statements for the vertical directrix.
 
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