已知xy=8满足x.x.y-x.y.y-x+y=5 - 知识问答

已知xy=8满足x.x.y-x.y.y-x+y=56.求x.x+y.y的值

2个回答

x.x.y-x.y.y-x+y
=xy(x-y)-(x-y)
=(xy-1)(x-y)
=7(x-y)=56
所以 x-y=8
x^2+y^2=(x-y)^2+2xy=64+16=80

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