数学题若M=(5x2-2x+3)-(3x2-3x),N=x2+x+2,早不知道x的值的情况下,你有办法比较M,N的大小吗

4个回答

  • 用作差法比较大小

    M-N

    =5x^2-2x+3-3x^2+3x-x^2-x-2

    =x^2+1≥1>0

    所以M>N

    A=-3x³+2x²-1,B=x³-2x²-x+4

    2A-(A-B)

    =2(-3x^3+2x^2-1)-(-3x^3+2x^2-1-x^3+2x^2+x-4)

    =-6x^3+4x^2-2-(-4x^3+4x^2+x-5)

    =-6x^3+4x^2-2+4x^3-4x^2-x+5

    =-2x^3-x+3

    当x=-1时,原式=-2×(-1)+1+3=6

    (-1/3a²b)-1/2ab²+(-1/4ba²)-(-2b²a)

    =-1/3a^2b-1/2ab^2-1/4a^2b+2ab^2

    =(-1/3-1/4)a^2b+(2-1/2)ab^2

    =-7/12a^2b+3/2ab^2

    3a²-【6a-(4a-3)-2a²】

    =3a^2-(6a-4a+3-2a^2)

    =3a^2-(-2a^2+2a+3)

    =3a^2+2a^2-2a-3

    =5a^2-2a-3