原式=1/(x-2)^2-1/(x+2)(x-2)+1/2(x+2)
=[2(x+2)-2(x-2)+(x-2)^2]/[2(x+2)(x-2)^2]
=(2x+4-2x+4+x^2-4x+4)/[2(x+2)(x-2)^2]
=(x^2-4x+12)/[2(x+2)(x-2)^2]