Question 467998
what is the directrix of 8x=y^2
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Standard form for given parabola; (y-k)^2=4p(x-h), with (h,k) being the (x,y) coordinates of the vertex.
For given parabola: y^2=8x
vertex is at origin (0,0), parabola opens rightwards
4p=8
p=4
Directrix is a vertical line 4 units from the vertex at x=-4
see graph below as a visual check on answer
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y=±(8x)^.5
{{{ graph( 300, 300, -10, 10, -10, 10,(8x)^.5,-(8x)^.5) }}}