先化简,再求值:3x²—[2x²y—(xy—x²)]+4x²y,其中x=—1,y=2.
问题描述:
先化简,再求值:3x²—[2x²y—(xy—x²)]+4x²y,其中x=—1,y=2.
答
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