Question

化简求值:2xy^2-[3xy^2-2(x^2y-(1/2)xy^2)]-2x^2y其中x=-2/3,y=-1/2

给分～

Answer 1

2xy^2-[3xy^2-2(x^2y-(1/2)xy^2)]-2x^2y
=2xy²-[4xy²-2x²y]-2x²y
=2xy²﹣4xy²﹢2x²y﹣2x²y
=﹣2xy²
=﹣2×﹙﹣2/3﹚﹙﹣1/2﹚
=﹣2/3

追问

﹣2×﹙﹣2/3﹚﹙﹣1/2﹚
(﹣1/2﹚不是平方吗

追答

漏了 2xy^2-[3xy^2-2(x^2y-(1/2)xy^2)]-2x^2y
=2xy²-[4xy²-2x²y]-2x²y
=2xy²﹣4xy²﹢2x²y﹣2x²y
=﹣2xy²
=﹣2×﹙﹣2/3﹚﹙﹣1/2﹚²
=1/3