f (x) = a(x - h)2 + k, where (h, k) is the vertex of the parabola. FYI: Different textbooks have different interpretations of the reference "standard form" of a quadratic function.
The standard form of a parabola is y=ax2++bx+c , where a≠0 . The vertex is the minimum or maximum point of a parabola. If a>0 , the vertex is the minimum point and the parabola opens upward. If a<0 , the vertex is the maximum point and the parabola opens downward.