A univariate (single-variable) quadratic function is one of the form f(x) = ax2 + bx + c, where a, b, and c are numbers with a not equal to zero. The graph of a quadratic function is a curve called a parabola. Parabolas may open upward or downward and vary in "width" or "steepness", but they all have the same basic "U" shape, whose axis of symmetry is parallel to the y-axis,

The app QFC:
calculates the roots of f(x)
draws the curve
calculates f(x) for a given x
calculates x for a given f(x)