已知(a+b)²=7,(a-b)²=3,求(1)x²+y² (2)xy的值
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已知(a+b)²=7,(a-b)²=3,求(1)x²+y² (2)xy的值
已知(a+b)²=7,(a-b)²=3,求(1)x²+y² (2)xy的值
已知(a+b)²=7,(a-b)²=3,求(1)x²+y² (2)xy的值
(x+y)²=7,(1)
(x-y)²=3,(2)
(1)+(2)
2(x²+y²)=10
x²+y²=5
(1)-(2)
4xy=4
xy=1
(1)x²+y²=5;(2)xy=1.