先化简再求值3x²y-[2xy²-2（xy-3/2 x²y）]+3xy²,其中x=3 y= -1/3
问题描述：
先化简再求值3x²y-[2xy²-2（xy-3/2 x²y）]+3xy²,其中x=3 y= -1/3
答
3x²y-[2xy²-2（xy-3/2 x²y）]+3xy²
=3x²y-（2xy²-2xy+3 x²y）+3xy²
=3x²y-2xy²+2xy-3 x²y+3xy²
=xy²+2xy
=xy（y+2）
x=3 y= -1/3 y=-1/9
x、y代进去得17/243
答
3x²y-[2xy²-2（xy-3/2 x²y）]+3xy²
=3x²y-（2xy²-2xy+3x²y）+3xy²
=3x²y-2xy²+2xy-3x²y+3xy²
=-2xy²+2xy+3xy²
=xy²+2xy
=xy(y+2) x=3,y=-1/3
=-1(-1/3+2)
=-5/3