(x²+1)(y²+1)=10x²y²+x²+y²+1=10x²y²-2xy+1+x²+y²+2xy=10(xy-1)²+(x+y)²=10[(xy-1)+(x+y)]²-2(x+y)(xy-1)=10(x+y)(xy-1)=3代入[(xy-1)+(x+y)]
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