计算.(1) 1+4 1 6 +7 1 12 +10 1 20 +13 1 30 +16 1 42 +19 1 56 +

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  • (1) 1+4

    1

    6 +7

    1

    12 +10

    1

    20 +13

    1

    30 +16

    1

    42 +19

    1

    56 +22

    1

    72 +25

    1

    90 ,

    =(1+4+7+10+13+16+19+22+25)+(

    1

    6 +

    1

    12 +

    1

    20 +

    1

    30 +

    1

    42 +

    1

    56 +

    1

    72 +

    1

    90 ),

    =117+(

    1

    2 -

    1

    3 +

    1

    3 -

    1

    4 +

    1

    4 -

    1

    5 +

    1

    5 -

    1

    6 +

    1

    6 -

    1

    7 +

    1

    7 -

    1

    8 +

    1

    8 -

    1

    9 +

    1

    9 -

    1

    10 ),

    =117+(

    1

    2 -

    1

    10 ),

    =117+

    2

    5 ,

    =117

    2

    5 ;

    (2)设

    17

    11 +

    18

    21 +

    19

    31 +

    20

    41 =a,

    18

    21 +

    19

    31 +

    20

    41 =b,则a-b=

    17

    11 +

    18

    21 +

    19

    31 +

    20

    41 -(

    18

    21 +

    19

    31 +

    20

    41 )=

    17

    11 ,那么:

    (

    17

    11 +

    18

    21 +

    19

    31 +

    20

    41 )×(

    18

    21 +

    19

    31 +

    20

    41 +

    21

    51 )-(

    17

    11 +

    18

    21 +

    19

    31 +

    20

    41 +

    21

    51 )×(

    18

    21 +

    19

    31 +

    20

    41 ) ,

    =a×(b+

    21

    51 )-(a+

    21

    51 )×b,

    =ab+

    21

    51 a-ab-

    21

    51 b,

    =

    21

    51 ×(a-b),

    =

    21

    51 ×

    17

    11 ,

    =

    7

    11 .