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

Toán Lớp 6: Cho A= 1+2^1+2^2+-+2^100+2^101. 7. Hỏi A chia 7 dư bao nhiêu? Giúp em với ak

Toán Lớp 6: Cho A= 1+2^1+2^2+….+2^100+2^101. 7. Hỏi A chia 7 dư bao nhiêu?
Giúp em với ak

Comments ( 2 )

  1. A = 1 + 2^1 + 2^2 + …. + 2^100 + 2^101
    A = (1 + 2^1 + 2^2) + …… + (2^99 + 2^100 + 2^101)
    A = 1(1 + 2^1 + 2^2) + ….. + 2^99(1 + 2^1 + 2^2)
    A = 1 . 7 + ……. + 2^99 . 7
    A = (1 + ……. + 2^99) . 7 \vdots 7 (Do 7 \vdots 7)
    Do A \vdots 7 nên A : 7 dư 0

  2.    A = 1 + 2 + 2^2 + … + 2^100 + 2^101
    ⇒ A = (1 + 2 + 2^2) + (2^3 + 2^4 + 2^5) + … + (2^99 + 2^100 + 2^101)
    ⇒ A = (1 + 2 + 2^2) + 2^3(1 + 2 + 2^2) + … + 2^99(1 + 2 + 2^2)
    ⇒ A = 7 + 2^3 . 7 + … + 2^99 . 7
    ⇒ A = (1 + 2^3 + … + 2^99) . 7
    Vì 7 vdots 7 ⇒ A vdots 7
    ⇒ A : 7 (dư 0)
     

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