解
3x²y-[2xy-2(xy-2/3x²y)+xy]
=3x²y-(2xy-2xy+4/3x²y+xy)
=3x²y-(4/3x²y+xy)
=5/3x²y-xy
=5/3×3²×(-1/3)-3×(-1/3)
=5/3×(-3)+1
=-5+1
=-4