The range of a function y = f(x) is the set of values y takes for all values of x within the domain of f. The graph of any quadratic function, of the form f(x) = a x2 + b x + c, which can be written in vertex form as follows. f(x) = a(x - h)2 + k where h = - b / 2a and k = f(h) is either a parabola opening up, when a > 0, or a parabola opening down, when a < 0
