2x^2-{-3x+[4x^2-（-x）^2-（2x^2-x）]},其中x=-2
=2x²+3x-4x²+x²+2x²-x
=x²+2x
=(-2)²+2*(-2)
=4-4
=0
当x=3,y=-3分之1时,求代数式3x^2y-[2xy^2-2（yx-2分之3x^2y）+xy]+3xy^2的值
3x^2y-[2xy^2-2（yx-2分之3x^2y）+xy]+3xy^2
=3x²y-2xy²+2xy--3x²y-xy+3xy²
=xy+xy²
=3*(-1/3)+3*(-1*3)²
=-1+1/3
=-2/3
已知A=2x^2-1,B=3-2x^2,求B-2（A-B）的值,其中x=-1
B-2(A-B)
=B-2A+2B
=-2A+3B
=-2*(2X²-1)+3*(3-2X²)
=-4X²+2+9-6X²
=-10X²+11
=-10*(-1)²+11
=-10+11
=1
100分拿来.