You can move from the second form to the first by expanding; you can move from the first to the second by completing the square or by using these formulas:
Assuming that a ≠ 0, the graph of a quadratic function is a shape called a parabola. The point (h, k) on the graph is called the vertex of the parabola. If a > 0, then the vertex gives the absolute minimum of the function; if a < 0, then the vertex gives the absolute maximum of the parabola. The parabola is symmetric, with a vertical line of symmetry whose equation is x = h. The roots (or zeroes) of the function are given by the quadratic formula:
In general, there are up to 7 useful points on the graph:
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