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问题: 13. 若x=根号2+1,y=根号2-1,求x²y-xy²分之(x-y)²的值。

解答:

x=√2+1,y=√2-1,则x-y=2,xy=1,
(x-y)²/(x²y-xy²)=4/{xy(x-y)}=4/2=2