A quadratic function is a function of the form 
. The vertex, 
of a quadratic function is determined by the formula: 
and 
; where 
is the x-coordinate of the vertex and 
is the y-coordinate of the vertex. The value of 
determines if the <span>parabola opens upward or downward; if</span> is positive, the parabola<span> opens upward and the vertex is the minimum value, but if </span> is negative <span>the graph opens downward and the vertex is the maximum value. Since the quadratic function only has one vertex, it </span><span>could not contain both a minimum vertex and a maximum vertex at the same time.</span>