先化简,再求值:3x²y-[2x²y-(xy²-x²y)-4xy²],？
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原式
=3x²y-(2x²y-xy²+x²y-4x²y)
=3x²y-(3x²y-4x²y-xy²)
=3x²y-(-x²y-xy²)
=3x²y+x²y+xy²
=4x²y+xy²
=xy(4x+y)
将x=-2 y=1/2带人
=-(4x-2+1/2)
=-(-8+1/2)
=7又(1/2),4,先化简,再求值:3x²y-[2x²y-(xy²-x²y)-4xy²],其中x=-2,y=1/2
=3x²y-(2x²y-xy²+x²y-4x²y)
=3x²y-(3x²y-4x²y-xy²)
=3x²y-(-x²y-xy²)
=3x²y+x²y+xy²
=4x²y+xy²
=xy(4x+y)
将x=-2 y=1/2带人
=-(4x-2+1/2)
=-(-8+1/2)
=7又(1/2),4,先化简,再求值:3x²y-[2x²y-(xy²-x²y)-4xy²],其中x=-2,y=1/2
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