1)3xy-4xy-(-2xy)

1个回答

  • 1.3xy-4xy-(-2xy)=3xy-4xy+2xy=(3-4+2)xy=xy

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

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

    =ab/3+a^2/12

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

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

    =6x^2-7x+2

    4.(3a-ab+7)-(-4a^2+2ab+7)

    =3a-ab+7-4a^2-2ab-7

    =-a^2-3ab+3a

    5.5(3a^2b-ab^2)-(ab^2+3a^2b)

    =15a^2b-5ab^2-ab^2-3a^2b

    =12a^2b-6ab^2

    当a=1/2,b=1/3时

    12a^2b-6ab^2

    =12×(1/2)^2×1/3-6×1/2×(1/3)^2

    =12×1/4×1/3-6×1/2×1/9

    =1-1/3

    =2/3