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