A minus 4 is less than or equal to zero, and the function scale is greater than or equal to zero. Solution: -2 is less than or equal to and A is less than or equal to 2.
A minus 4 is greater than zero, the function has two intersections, and the symmetry axis is on the left side of the origin: the right intersection of the function and the X axis should be on the left side of the origin, and find a root X2 of the function to make it less than 0; Symmetry axis is on the right side of the origin: the left intersection of the function and the X axis should be on the right side of the origin. Solve one of the functions with X 1 to make it greater than zero. In short, x=0 and = 1/2 cannot be distributed on both sides of the symmetry axis and the intersection point.