Question 475247
The standard form of the parabola is {{{4c(x-h) = (y-k)^2}}}, where (h,k) is the vertex, and c is the directed distance between the focus and the vertex.
==> the vertex is (0,0), the equation is equivalent to {{{4x = y^2}}}, and 4c = 4.
==> c = 1.

Since the directrix has the same (absolute) distance as the focus from the vertex, but located on the opposite side of the vertex, the directrix is the (vertical) line x = -1.