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

Toán Lớp 6: CMR: A = (1 + 2 + 2^2 + 2^3 +…+ 2^2008) không chia hết cho 7

Toán Lớp 6: CMR: A = (1 + 2 + 2^2 + 2^3 +…+ 2^2008) không chia hết cho 7

Comments ( 1 )

  1. A=1+2+2^2+2^3+. . .+2^2008
    A=(1+2+2^2)+(2^3+2^4+2^5)+. . .+(2^2004+2^2005+2^2006)+(2^2007+2^2008)
    A=7+2^3 . (1+2+2^2)+. . .+2^2004.(1+2+2^2)+2^2007.(1+2)
    A=7+2^3 . 7 + . . . + 2^2004 . 7 + 2^2007 . 3
    A=7.(1+2^3+. . .+2^2004)+2^2007 . 3
    Vì 7.(1+2^3+. . .+2^2004) vdots 7
         2^2007 . 3 \cancel{vdots} 7
    ⇒A \cancel{vdots} 7

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