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

Toán Lớp 6: Cho M = 1+ 3+32 + 33 + 34 + …+ 399 . Chứng tỏ M chia hết cho 13.

Toán Lớp 6: Cho M = 1+ 3+32 + 33 + 34 + …+ 399 . Chứng tỏ M chia hết cho 13.

Comments ( 2 )

  1. $\text{M = 1 + 3 + $3^2$ + $3^3$ + $3^4$ +…+ $3^{99}$}$
    $\text{M = ( 1+ 3 + $3^2$ ) + ( $3^3$ + $3^4$ + $3^5$ ) + … + ( $3^{97}$ + $3^{98}$ + $3^{99}$ )}$
    $\text{M = 13 + $3^3$ ( 1 + 3 + $3^2$ ) + …. + $3^{97}$ ( 1 + 3 + $3^2$ ) }$
    $\text{M = 13 + $3^3$ . 13 + …. + $3^{97}$ . 13}$
    $\text{M = 13 ( 1 + $3^3$ + … + $3^{97}$ ) $\vdots$ 13 ( vì 13 $\vdots$ 13 )}$
    $\text{    Vậy M $\vdots$ 13}$

  2. M = 1+ 3+32 + 33 + 34 + …+ 399
    M=(1+3+3^2)+(3^3+3^4+3^5)+….+(3^97+3^98+3^99)
    M=1×(1+3+9)+3^3×(1+3+9)+…+3^97.(1+3+9)
    M=1×13+3^3×13+….+3^97×13
    M=(1+3^3+…+3^97)×13 $\vdots$ 13
    => M$\vdots$ 13 (ĐPCM)
                                            

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

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