parabola question

[Guest]

determine the coordinates of the vertex and the focus, and the equation of the directrix.


I didn't get this one: x-3= 1/2(y+1)^2

I thought the directriz would be -.5, but it apparently isn't correct according to the book.. the book says its 2.5

 

[Gene]

If you put it in standard form then
(y-k)^2=4p(x-h)
the vertex is P(h,k)
the directrix is x = h-p and the focus is P(h+p,k).
The standard form of this equation is
(y+1)^2 = 4(1/2)(x-3)