x/(x-y+z)+(2x+2z)/(y-x-z)-(y+z)/(y-x-z)
＝x/(x-y+z)-(2x+2z)/(x-y+z)+(y+z)/(x-y+z)
=(x-2x-2z+y+z)/(x-y+z)
=(-x+y-z)/(x-y+z)
=-1计算：[a²+b²/a²-b²-(a-b)/a+b]×(a-b)/2a、、、、、求过程