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(1)x²y+xy²
=xy(x+y)
∵x+y=2，xy=2/3
∴原式=2/3×2=4/3
(2)(x²-1)(y²-1)
=x²y²-x²-y²+1
=(xy)²-(x²+y²)+1
=(xy)²-(x²+y²+2xy-2xy)+1
=(xy)²-(x+y)²+2xy+1
=(2/3)²-2²+2×2/3+1
=4/9-4+4/3+1
=-11/9
=xy(x+y)
∵x+y=2，xy=2/3
∴原式=2/3×2=4/3
(2)(x²-1)(y²-1)
=x²y²-x²-y²+1
=(xy)²-(x²+y²)+1
=(xy)²-(x²+y²+2xy-2xy)+1
=(xy)²-(x+y)²+2xy+1
=(2/3)²-2²+2×2/3+1
=4/9-4+4/3+1
=-11/9
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