化简并求值 xy-2{xy-[3x²y-(xy²+0.5xy)]+4x²y},其中x=1,y=-2

xy-2{xy-[3x²y-(xy²+0.5xy)]+4x²y}
=xy-2[xy-(3x²y-xy²-0.5xy)+4x²y]
=xy-2(xy-3x²y+xy²+0.5xy+4x²y)
=xy-2xy+6x²y-2xy²-xy-8x²y
=-2xy-2x²y-2xy²
=-2*1*(-2)-2*1*(-2)-2*1*4
=4+4-8
=0