y= x^2/4
the focus is the same distance from the vertex as the directrix, so the directrix is y=-1
find the point horizontally across from the focus on the parabola that's equidistant to the directrix
that point is (2,1) (2,1) to the focus is a distance 2, same as from y=1 to y=-1
the general formula for the parabola is y=ax^2
plug in that point (2,1) to get
1 = a(2^2)
1 = 4a
a = 1/4
so the parabola equation is
y= (1/4)x^2 or
multiply through by 4 to get
4y = x^2
