已知x=3 y=1\3,求3x²y-[2xy²-2﹙xy-3\2x²y﹚+xy]+3xy²
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已知x=3 y=1\3,求3x²y-[2xy²-2﹙xy-3\2x²y﹚+xy]+3xy²
已知x=3 y=1\3,求3x²y-[2xy²-2﹙xy-3\2x²y﹚+xy]+3xy²
已知x=3 y=1\3,求3x²y-[2xy²-2﹙xy-3\2x²y﹚+xy]+3xy²
解 原式=3x²y-[2xy²-2﹙xy-3\2x²y﹚+xy]+3xy²
=3x²y-[2xy²-2xy+3x²y+xy]+3xy²
=3x²y-2xy²+2xy - 3x²y - xy+3xy²
=xy²+xy
将x=3 y=1\3 代入上式
得 3 ×(1/3)²+3×1/3
= 1/3+1
= 4/3