Toán Lớp 6: Cho S= 1+3+3^2+3^3+3^4+3^5+3^6+3^7+3^8+3^9 Chứng tỏ rằng x chia hết cho 4

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1. S=4+9+27+81+243+729+2187+6561+19683 =29524 =>29524÷4=7381 Vậy S chia hết cho 4

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2. $\text{S = 1 + 3 + $3^2$ + $3^3$ + $3^4$ + $3^5$ + $3^6$ + $3^7$ +$3^8$ + $3^9$ }$

   $\text{S = (1 + 3 ) + ( $3^2$ + $3^3$ ) + ( $3^4$ + $3^5$ ) + ( $3^6$ + $3^7$ ) + ( $3^8$ + $3^9$ )  }$

   $\text{S = 4 + $3^2$ ( 1 + 3 ) + $3^3$ ( 1 + 3) + … + $3^8$ ( 1 + 3 )}$

   $\text{S = 4 + $3^2$ .4 + $3^3$ . 4 + … + $3^8$ . 4 )}$

   $\text{S = 4 ( 1 + $3^2$ + $3^3$ + … + $3^8$ ) $\vdots$ 4 ( vì 4 $\vdots$ 4 )}$

   $\text{ Vậy S $\vdots$ 4}$

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