当x=1/2时
2x的2次方-4x/x+2×x的2次方+2x/x的2次方-4x+4+4x/2-x
=[2x（x-2)/(x+2)][2x(x+2)/(x-2)²]-4x/(x-2)
=4x²/(x-2)-4x/(x-2)
=4x(x-1)/（x-2）
=2(-1/2)/(-3/2)
=2/3