Write an equation of a parabola that opens downward, has a vertex at the origin, and a focus at (0, –1).

Step-by-step explanation:

The general equation of parabola :

    (i)

where (h,k) = vertex of parabola

Focus = (h,k+p)

When p<0 , the parabola opens downwards.

As per given  , (h,k) = (0,0)

focus =  (0, –1).

i.e. h=0 , k=0 , k+p=-1 , i.e. p=-1

On substituting the value of h , k and p in (i) , we get

Equation of a parabola that opens downward, has a vertex at the origin, and a focus at (0, –1) :

you probably already have the answer but anyways it's b. 15.0

step-by-step explanation: