The equation is written:
[tex]y = (x - h)^2 + k[/tex]
where h is the x coordinate of the vertex and k is the y coordinate of the vertex
So we just put it in the equation:
[tex]y=x^2[/tex]
And thus if [tex]y=-1[/tex], then [tex]x=i[/tex], where [tex]i= \sqrt{-1} [/tex]
