A parabola opening up or down has vertex (0,4) and passes through ( - 10, - 1). Write its equation in vertex form.

Ok...so we have this........

y = ax² + 4      ....... and we need to find "a"

So we have

-1 = a(-10)² + 4

-5 = a (100)

(-1/20) = a      .......  So we have ..........

y = (-1/20)(x- 0)² + 4   or just  (-1/20)x² + 4

Note that this parabola opens downward...That makes sense since the vertex is above the x axis and the parabola passes through a point below the x axis.

It's right if b= 0 !

Opening up or down implies that the axis of symmetry is parallel to the y axis.

CPhill's  answer is the only possible answer!