So for the sake of understanding, let's make a symmetrical point A0(x0, y0) about the axis of symmetry, and we can easily get that x 1+x0=4, then x 1+x2 is greater than 4, that is, x 1+x2 is greater than x 1+x0. A and A0 are as far away from the symmetry axis, so isn't B farther than A?