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

Toán Lớp 6: chứng minh rằng A=2 + 2^2 +2^3+ 2^4 +…+ 2^100 chia hết cho 3

Toán Lớp 6: chứng minh rằng A=2 + 2^2 +2^3+ 2^4 +…+ 2^100 chia hết cho 3

Comments ( 2 )

  1. A=2 + 2^2 +2^3+ 2^4 +…+ 2^100
    ->A=\underbrace{(2+2^2)+(2^3+2^4)+…+(2^99+2^100)}_{50 text{cặp}}
    ->A=2(1+2)+2^3(1+2)+…+2^99(1+2)
    ->A=2. 3+2^3 . 3+…+2^99 . 3
    ->A=3.(2+2^3+2^99)\vdots3
    ->A\vdots3
    Vậy A\vdots3

  2. A=2+2^2+2^3+2^4+. . .+2^100
    A=(2+2^2)+(2^3+2^4)+. . .+(2^99+2^100)
    A=2.(1+2)+2^3.(1+2)+. . .+2^99.(1+2)
    A=2.3+2^3 . 3 + . . .+2^99 . 3
    A=3.(2+2^3+. . .+2^99)
    ⇒A vdots 3

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

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