先化简,再求值:3x²y-[2x²y-(xy²-x²y)-4xy²],其中x=-2,y=1/2

先化简,再求值:3x²y-[2x²y-(xy²-x²y)-4xy²],其中x=-2,y=1/2
先化简,再求值:3x²y-[2x²y-(xy²-x²y)-4xy²],其中x=-2,y=1/2

先化简,再求值:3x²y-[2x²y-(xy²-x²y)-4xy²],其中x=-2,y=1/2
3x²y-[2x²y-(xy²-x²y)-4xy²],其中x=-2,y=1/2
=3x²y-2x²y+xy²-x²y+4xy²
=5xy²
=5×(-1)×1/4
=-5/2;
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3x²y-[2x²y-(xy²-x²y)-4xy²]
=3x²y-2x²y+(xy²-x²y)+4xy²
=5xy²
代入x=-2,y=1/2
5xy²=5*（-2）*（1/2)²=-5/2

3x²y-[2x²y-(xy²-x²y)-4xy²]
=3x²y-2x²y+xy²-x²y+4xy²
=5xy²
=5*(-2)*1/4
=-5/2