当x=3,y=-1/3时求代数式3x*xy-[2xy*y-2(xy-2/3x*xy)+xy]+3xy*y的值

当x=3,y=-1/3时求代数式3x*xy-[2xy*y-2(xy-2/3x*xy)+xy]+3xy*y的值
当x=3,y=-1/3时求代数式3x*xy-[2xy*y-2(xy-2/3x*xy)+xy]+3xy*y的值

当x=3,y=-1/3时求代数式3x*xy-[2xy*y-2(xy-2/3x*xy)+xy]+3xy*y的值
=3x^2y-2xy^2+2(xy-3/2x^2y)-xy+3xy^2
=3x^2y+xy^2+2xy-3x^2y-xy
=xy+xy^2
=3*(-1/3)+3*1/9
=-2/3

3x*xy-[2xy*y-2(xy-2/3x*xy)+xy]+3xy*y
=3x^2y-2xy^2+2xy-2/3x^2y-xy+3xy^2
=7/3x^2y+xy^2+xy
当x=3,y=-1/3时,原式=7/3*3^2*(-1/3)+3*(-1/3)^2+3*(-1/3)
=-7+1/3-1
=-23/3

x=3,y=-1/3
xy=-1
代入3x*xy-[2xy*y-2(xy-2/3x*xy)+xy]+3xy*y
=-3x-[-2y-2(-1-2)/(-3x)-1]-3y
=-3x-[-2y-2/x-1]-3y
=-3x+2y+2/x+1-3y
=-3x+2/x+1-y
=-3x+(2+x-2xy)/x
=-3x+(2+x+2)/x
=-3x+4/x+1
=-9+4/3+1
=-20/3

先化简=xy(5/3x+y+1).最后代入=-11/3