3x^2y-[2xy-2(xy-2/3x^2y)+xy],其中x=3,y=-3/1.等于

问题描述:

3x^2y-[2xy-2(xy-2/3x^2y)+xy],其中x=3,y=-3/1.等于

3x²y-[2xy-2(xy-2/3x²y)+xy]
=3x²y﹣3x²y﹣xy
=﹣xy
=﹣3×﹙﹣1/3﹚
=1

∵x=3,y=-3/1(此处应为:y=-1/3)
3x^2y-[2xy-2(xy-2/3x^2y)+xy]=3x²y-2xy+2xy-4x²y/3-xy=5x²y/3-xy=5×3²×(-1/3)/3-3×(-1/3)=-5+1=-4

先化简,再求值3x²y-[2xy-2(xy-2/3x²y)+xy]=3x²y-2xy+2(xy-2/3x²y)-xy=3x²y-2xy+2xy-4/3x²y-xy=5/3x²y-xy=xy(5/3x-1)将x=3,y=-1/3 代入原式=xy(5/3x-1)=3×(-1/3)(5/3×3-1)=-1×...