Quadratic functions

A quadratic function f may be written in either of two forms:

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 (hk) on the graph is called the vertex of the parabola. If a > 0, then the vertex is the lowest point on the parabola; if a < 0, then the vertex is the highest point on the parabola. The parabola is symmetric, with a vertical line of symmetry whose equation is x = h. The zeroes of the function are given by the quadratic formula:

However, these will be imaginary numbers if b2 − 4ac is negative.

In general, there are up to 7 useful points on the graph:

The last two won't exist on the graph if z± are imaginary.
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