## Precalculus (6th Edition) Blitzer

Focus is: $(0,-1)$ and directrix is: $y=1$; $\bf{Graph (b)}$
Standard form of a parabola is given as: $x^2=4py$ ...(1) Formula to find focus is: $F(0,p)$ and formula to find directrix is: $y=-p$ As we are given that $x^2=-4y$ Compare this form with the equation (1), we have: $p=-1$ Thus, Focus is: $(0,-1)$ and directrix is: $y=1$ All the above information matches to the $\bf{Graph (b)}$