化简求值,请选择一个你喜欢的x或者a、b值,代入求值.

1个回答

  • (1)原式=(

    x-1

    x-1 +

    1

    x-1 )•

    (x-1)(x+1)

    x

    =

    x

    x-1 •

    (x-1)(x+1)

    x

    =x+1;

    当x=2时,原式=2+1=3;

    (2)原式=

    1

    2 a+1-a+

    (a-1)(a+1)

    (a-1)

    =

    1

    2 a+1-a+a+1

    =

    1

    2 a+2;

    当a=2时,原式=

    1

    2 ×2+2=3;

    (3)原式= (

    x-1

    x+1 +

    1

    x 2 -1 )•( x 2 -1)

    = (

    x-1

    x+1 +

    1

    x 2 -1 )•(x-1)(x+1)

    =

    x-1

    x+1 •(x-1)(x+1)+

    1

    (x-1)(x+1) (x-1)(x+1)

    =(x-1) 2+1

    =x 2-2x+1+1

    =x 2-2x+2;

    当x=2时,原式=2 2-2×2+2

    =4-4+2

    =2;

    (4)原式=

    a 2 -2a+1

    a •

    a(a+1)

    (1-a)(1+a)

    =

    (a-1 ) 2

    a •

    a(a+1)

    (1-a)(1+a)

    =1-a;

    当x=2时,原式=1-2=-1;

    (5)原式=

    a-b

    a+2b •

    (a+2b ) 2

    (a-b)(a+b) -1

    =

    a+2b

    a+b -1

    =

    a+2b-a-b

    a+b

    =

    b

    a+b ;

    当a=1,b=2时,原式=

    2

    1+2 =

    2

    3 .