If f (x) and g (x) are a quadratic functions but (f + g) (x) produces the graph below,

Thus, the standardized form of a quadratic equation is ax2 + bx + c = 0, where "a" does not ... We said that the graph of y = x2 was a function because it passed the vertical line test ... Find the vertex of the parabola y = 2x2 - 12x + 7 ... To find the y-value, we would substitute 3 in for x, or find f (3) = 2 (3) 2 - 12 (3) + 7 = - 11.