0.2x²y-1/2xy²+3/2y²x-3/4x²y
=0.2x²y-1/2xy²+3/2xy²-3/4x²y
=(0.2x²y-3/4x²y)+(3/2xy²-1/2xy²)
=-0.55x²y+xy²
=xy(-0.55x+y)
=-2×（-3）×[-0.55×（-2）-3]
=6×[1.1-3]
=6×(-1.9)
=-11.4