Is y=2x(x-2) a quadratic function

The graph opens downward, so the vertex is the maximum point of the parabola. Example: The vertex of the parabola y = -(x + 9)2 + 4 is (-9, 4). The graph opens downward, so the vertex is the maximum point of the parabola.
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If the value of "a" is positive, the parabola will open upward.