
已知x+y=根号下3倍根号5-根号2,x-y=根号下3倍根号2-根号5,求xy值
1个回答
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第一个是3√5+√2吧
(x+y)²-(x-y)²
=(x+y+x-y)(x+y-x+y)
=4xy
所以xy=[(x+y)²-(x-y)²]/4
=(3√5+√2-3√5+√2)/4
=√2/2
(x+y)²-(x-y)²
=(x+y+x-y)(x+y-x+y)
=4xy
所以xy=[(x+y)²-(x-y)²]/4
=(3√5+√2-3√5+√2)/4
=√2/2
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