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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 5: 1/3 + 1/6 + 1/10 + … + 1/X nhân ( x + 1 ) : 2 = 2009/2011 em chịu hoy

Toán Lớp 5: 1/3 + 1/6 + 1/10 + … + 1/X nhân ( x + 1 ) : 2 = 2009/2011
em chịu hoy

Comments ( 2 )

  1.  text{Giải đáp + Lời giải và giải thích chi tiết :}
    1/3 + 1/6 + 1/10 + … + 1/(x xx(x+1):2) = 2009/2011
    2/6 + 2/12 + 2/20 + … + 2/(x xx(x+1) = 2009/2011
    2/(2xx3) + 2/(3xx4) + 2/(4xx5) + … + 2/(x xx(x+1) = 2009/2011
    ( 2/(2xx3) + 2/(3xx4) + 2/(4xx5) + … + 2/(x xx(x+1) : 2 = 2009/2011 : 2
    1/2xx3 + 1/3xx4 + 1/4xx5 + … + 1/x xx(x+1) = 2009/4022
    1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + … + 1/x – 1/(x+1) = 2009/4022 
    1/2 – 1/(x+1) = 2009/4022 
    1/(x+1) = 1/2 – 2009/4022 
    1/(x+1) = 1/2011
    x + 1 = 2011
    x = 2011 – 1
    x = 2010
    -> x = 2010 .
    text{@muoiakiramobile}

  2. 1/3 + 1/6 + 1/10 + ……………. + 1/(x xx(x+1):2) = 2009/2011
    -> 2/6 + 2/12 + 2/20 + ………… + 2/(x xx(x+1) = 2009/2011
    2 xx ( 1/6 + 1/12 + 1/20 + …………. + 1/(x xx(x+1) = 2009/2011
    2 xx ( 1/(2xx3) + 1/(3xx4) + 1/(4xx5) + ……………. 1/(x xx(x+1) ) = 2009/2011
    2 xx ( 1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + ………… 1/x – 1/(x+1) = 2009/2011
    2 xx ( 1/2 – 1/(x+1) ) = 2009/2011
    1/2 – 1/(x+1) = 2009/2011 : 2
    1/2 – 1/(x+1) = 2009/4022
    1/(x+1) = 1/2 – 2009/4022
    1/(x+1) = 1/2011
    -> x + 1 = 2011
    x = 2011 – 1
    x = 2010
    $\text{-> Vậy x = 2010}$

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222-9+11+12:2*14+14 = ? ( )

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