Chapter 11 - Section 11.1 - Parabolas - 11.1 Exercises - Page 788: 21

(a) Focus: $F(0,-3)$ Directrix: $y=3$ $Focal~diameter=12$ (b)

Equation of a parabola with vertical axis: $x^2=4py$ $x^2+12y=0$ $x^2=-12y$ $4p=-12$ $p=-3$ Focus: $F(0,p)=F(0,-3)$ Directrix: $y=-p=3$ $Focal~diameter=|4p|=12$