Derive the equation of the parabola with a focus at (-2, 4) and a directrix of y=6. Put the equation in standard form.
a. f(x)=1/4​x²−x+4
b. f(x)=−1/4​x²−x+4
c. f(x)=1/4x²−x−5
d. f(x)=−1/4​x²−x−5