化简求职:2xy^2-[3xy^2-2(x^2y-(1/2)xy^2)]-2x^2y其中x=-2/3,y=-1/2
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你好：
2xy²-[3xy²-2(x²y-(1/2)xy²)]-2x²y
=（2-3）xy²+2x²y+(1/2)xy²-2x²y
=(1/2)xy²-xy²
=-(1/2)xy²
x=-2/3,y=-1/2
带入，得
-(1/2)×-2/3×（-1/2）²
=1/12
2xy²-[3xy²-2(x²y-(1/2)xy²)]-2x²y
=（2-3）xy²+2x²y+(1/2)xy²-2x²y
=(1/2)xy²-xy²
=-(1/2)xy²
x=-2/3,y=-1/2
带入，得
-(1/2)×-2/3×（-1/2）²
=1/12
追问
2(x²y-(1/2)xy²的2x²y+(1/2)xy²不应该是＋xy吗，乘以2
追答
奥
2xy²-[3xy²-2(x²y-(1/2)xy²)]-2x²y
=（2-3）xy²+2x²y-2×(1/2)xy²-2x²y
=-xy²-xy²
=-2xy²
x=-2/3,y=-1/2
带入，得-2×（-2/3）×（-1/2）²=1/3
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