化简求值:(1)2x²-y²+(2y²-x²)-(x²+2y²),其中x=3分之1,y=3

问题描述:

化简求值:(1)2x²-y²+(2y²-x²)-(x²+2y²),其中x=3分之1,y=3
(2)5(3x²y-xy²)-(xy²-3x²y),其中x=2分之1,y=-1

  (1)2x²-y²+(2y²-x²)-(x²+2y²)
  =2x²-y²+2y²-x²-x²-2y²
  =-y²
  =-9
  (2)5(3x²y-xy²)-(xy²-3x²y)
  =6(3x²y-xy²)
  =6xy(3x-y)
  =-3(3/2+1)
  =-15/2
  很高兴为你答疑,