Derive the equation of the parabola with a focus at (2, −1) and a directrix of y = −one half

Derive the equation of the parabola with a focus at (2, −1) and a directrix of y = −one half.

a. f(x) = −(x + 2)2 − three fourths
b. f(x) = (x + 2)2 + three fourths
c. f(x) = −(x − 2)2 + three fourths
d. f(x) = −(x − 2)2 − three fourths