Quadratic equations. Provided , the solutions of a quadratic equation are given by
Parabola. The graph of an equation with leading coefficient represents a parabola. It opens upward if , or downward if . The lowest point of an upward parabola is called the vertex of the parabola. Likewise, the vertex of a downward parabola is the highest point.
Quadratic functions. A function is called a quadratic function if
Standard equations of parabola. The quadratic function (4) is also written in the form