`Tính bằng cách hợp lí a/1+3+5+7+9+…+2013 b/100+98+96+…+2-97-95-…-1 c/1+2+3+4+…+n d/2.3.12+4.6.42+8.27.3

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`Tính bằng cách hợp lí
a/1+3+5+7+9+…+2013
b/100+98+96+…+2-97-95-…-1
c/1+2+3+4+…+n
d/2.3.12+4.6.42+8.27.3

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Huy Gia 5 years 2020-11-30T16:07:47+00:00 1 Answers 124 views 0

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  1. Edana
    0
    2020-11-30T16:09:28+00:00
    Reply

    a) 1+3+5+7+…+2013

    =(2013+1)+(2011+3)+…+(1009+1005)+1007

    =2014+2014+…+2014+1007

    =2014*1007+1007

    =2015*1007

    =2 029 105

    b)100+98+96+…+2-97-95-…-1

    =(98-97)+(96-95)+…+(2-1)+100

    =1+1+1+…+1+100

    =1*49+100

    =49+100

    =149

    c)1+2+3+4+…+n

    =(n+1)+(n-1+2)+(n-2+3)+…

    =n+1+n+1+n+1+…

    d)2.3.12+4.6.42+8.27.3

    =(2*12)*3+(4*6)*42+(8*3)*27

    =24*3+24*42+24*27

    =24*(3+27+42)

    =24*72

    =1728

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