Determine the opening direction and size of parabola. When a > 0, the parabola opens upwards, and when a < 0, the parabola opens downwards. B and a*** both determine the position of the axis of symmetry. When the symbols of A and B are the same (that is, AB > 0), the symmetry axis is on the left side of the Y axis, and when the symbols of A and B are different (that is, AB < 0), the symmetry axis is on the right side of the Y axis. C determines the intersection of parabola and y axis, and parabola and y axis intersect at (0, c).