So hmm check the picture below
we know the vertex is at the origin, and the focus point is below it, that means two things, the parabola is vertical and it's opening downwards
notice the distance "p", from the vertex to the focus point, is just 7 units, however, since the parabola is opening downwards, the "p" value will be negative, so p = -7
we know the vertex is at the origin, and the focus point is below it, that means two things, the parabola is vertical and it's opening downwards
notice the distance "p", from the vertex to the focus point, is just 7 units, however, since the parabola is opening downwards, the "p" value will be negative, so p = -7