Question: when graphed which parabola opens downward?
Answer: If a<0 in f(x)=ax2+bx+c, the parabola opens downward. In this case the vertex is the maximum, or highest point, of the parabola. Again, a large negative value of a makes the parabola narrow; a value close to zero makes it wide. For an equation in standard form, the value of c gives the y-intercept of the graph.