1.x+y=4,x²-y²=20,则x-y=多少?2.已知x+y=3,xy=2,求x²+y²的值1.x+y=4,x²-y²=20,则x-y=多少?2.已知x+y=3,xy=2,求x²+y²的值3.已知x-y=5,x²+y²=15,求xy的值4.已知（a+b）²=17,ab=3.求（

1.x+y=4,x²-y²=20,则x-y=多少?2.已知x+y=3,xy=2,求x²+y²的值1.x+y=4,x²-y²=20,则x-y=多少?2.已知x+y=3,xy=2,求x²+y²的值3.已知x-y=5,x²+y²=15,求xy的值4.已知（a+b）²=17,ab=3.求（
1.x+y=4,x²-y²=20,则x-y=多少?2.已知x+y=3,xy=2,求x²+y²的值
1.x+y=4,x²-y²=20,则x-y=多少?
2.已知x+y=3,xy=2,求x²+y²的值
3.已知x-y=5,x²+y²=15,求xy的值
4.已知（a+b）²=17,ab=3.求（a-b）²的值

1.x+y=4,x²-y²=20,则x-y=多少?2.已知x+y=3,xy=2,求x²+y²的值1.x+y=4,x²-y²=20,则x-y=多少?2.已知x+y=3,xy=2,求x²+y²的值3.已知x-y=5,x²+y²=15,求xy的值4.已知（a+b）²=17,ab=3.求（
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