2x²y-[3xy²-2(xy-kx²y)+3xy]+3xy²
=2x²y-3xy²+2xy-2kx²y-3xy+3xy²
=2x²y-2kx²y-xy
因为不含3次项,
因此2x²y-2kx²y=0
因此2k=2
因此k=1