化简：3x²—[2x²y—（xy—x²）]+4x²y
=3x²-（2x²y-xy+x²）+4x²y
=3x²-2x²y+xy-x²+4x²y
=2x²+2x²y+xy
将x=-1,y=2 代入代数式中,得：2x²+2x²y+xy=4