3x²y-{2x²y-3(2xy-x²y-x²y)-xy}

问题描述:

3x²y-{2x²y-3(2xy-x²y-x²y)-xy}

3x²y-{2x²y-3(2xy-x²y-x²y)-xy}=3x²y-2x²y+3(2xy-2x²y)+xy=x²y+6xy-6x²y+xy=x²y-6x²y+6xy+xy=-5x²y+7xy