Chapter 11 - Section 11.1 - Parabolas - 11.1 Exercises - Page 788: 15

(a) Focus: $F(0,-2)$ Directrix: $y=2$ $Focal~diameter=8$ (b)

Equation of a parabola with vertical axis: $x^2=4py$ $y=-\frac{1}{8}x^2$ $x^2=-8y$ $4p=-8$ $p=-2$ Focus: $F(0,p)=F(0,-2)$ Directrix: $y=-p=2$ $Focal~diameter=|4p|=8$