have a vertex at (-4,-1) with a vertical axis of symennetry. which one has a directrix of y=-4

so far i got (x+4)^2=?(y+1)

what is the ?..?!! how do i get that

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- Apr 19th 2009, 04:55 PMpeekybooyoudirectrix of y=-4
have a vertex at (-4,-1) with a vertical axis of symennetry. which one has a directrix of y=-4

so far i got (x+4)^2=?(y+1)

what is the ?..?!! how do i get that - Apr 19th 2009, 10:51 PMGrandadDirectrix of a parabola
Hello peekybooyouYou're right so far. You have used the fact that the parabola has vertex at and a vertical axis of symmetry. You've replaced by and by to give a parabola whose vertex is at .

Now you need to use the fact that the parabola has directrix .

If in the coordinates, the directrix is , in the coordinates it is

So in coordinates the equation is ; in coordinates it is

Grandad