Question

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
正确答案-5/2，求过程

Answer 1

3x²y-[2x²y-(xy²冲陆基-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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Answer 2

3x²y-[2x²y-(xy²悄伍陆-x²y)-4xy²]
=3x²启顷y-2x²y+xy²-x²y+4xy²
=5xy²
=5*(-2)*1/4
=-5/橘举2

Answer 3

3x²y-[2x²y-(xy²-x²y)-4xy²]
=3x²郑敬虚y-2x²y+(xy²-x²y)+4xy²
=5xy²稿悉
代入x=-2,y=1/2
5xy²=5*（-2）*（喊燃1/2)²=-5/2