Answer
Look at the value of a.
Work Step by Step
We know that parabolas follow the form $y=ax^2+bx+c$. Thus, once the parabola is in this form, we can graph it. After all, we know that $-\frac{b}{2a}$ is the vertex, and c is the y-intercept. Also, if a is positive, the graph opens up, while if a is negative, the graph opens down. Knowing this, we create the graph. Thus, the value of a determines whether it is a maximum or a minimum at the vertex.
