解答：x＝1－√2，y＝√2＋1∴x－y＝1－√2－√2－1＝－2√2.－x²＋2xy－y²＝－(x²－2xy＋y²)＝－(x－y)²＝－(2√2)²＝－8.有疑问，欢迎追问！
-x²+2xy-y²=-(x-y)^2=-(2√2)^2=-8
