tính nhanh a,A=5-10+15-20+…+2005-2010 b,1-2-3+4+5-6-7+8+…+2000+2001-2002

Question

tính nhanh a,A=5-10+15-20+…+2005-2010
b,1-2-3+4+5-6-7+8+…+2000+2001-2002

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aihong 1 năm 2021-07-24T01:37:02+00:00 2 Answers 7 views 0

Answers ( )

    0
    2021-07-24T01:38:03+00:00

    Bạn tham khảo :

     $A= 5 – 10 + 15 – 20 +…+2005-2010$

     $A= (5 – 10 )+ (15 – 20) +…+(2005-2010)$

     $A= -5 . 201$

     $A = -1005$ 

    $1 – 2 – 3 + 4 +5 – 6 – 7 + 8 +…+ 2000 + 2001 – 2002$

    $=(1 – 2 – 3)+( 4 +5 – 6 – 7) +(8 +9 – 10 – 11) + …+( 1996 + 1997 – 1998 – 1999)+( 2000+ 2001 – 2002)$              

    $= 500 . (-4)+ 1999$

    $= -2000 + 1999$

    $= -1$

     

    0
    2021-07-24T01:38:44+00:00

    a/ A= 5 – 10 + 15 – 20 +…+2005-2010

        A= (5 – 10 )+ (15 – 20) +…+(2005-2010)

                               201 cặp

       A= -5 . 201

       A = -1005

    Vậy A = – 1005

    b/1 – 2 – 3 + 4 +5 – 6 – 7 + 8 +…+ 2000 + 2001 – 2002

    =(1 – 2 – 3)+( 4 +5 – 6 – 7) +(8 +9 – 10 – 11) + …+( 1996 + 1997 – 1998 – 1999)+( 2000+ 2001 – 2002)

                                                           500 cặp

    = -4 . 500 + 1999

    = -2000 + 1999

    = -1

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