cho C=1+3+32+33+...+311
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(C=1+3+3^2+3^3+...+3^{11}\\ a,C=\left(1+3+3^2\right)+\left(3^3+3^4+3^5\right)+\left(3^6+3^7+3^8\right)+\left(3^9+3^{10}+3^{11}\right)\\ =13+3^3.\left(1+3+3^2\right)+3^6.\left(1+3+3^2\right)+3^9.\left(1+3+3^2\right)\\ =13+3^3.13+3^6.13+3^9.13\\ =13.\left(1+3^3+3^6+3^9\right)⋮13\)
Ý a phải chia hết cho 13 chứ em?
b: C=(1+3+3^2+3^3)+...+3^8(1+3+3^2+3^3)
=40(1+...+3^8) chia hết cho 40
a: C ko chia hết cho 15 nha bạn
![](https://rs.olm.vn/images/avt/0.png?1311)
a, C = 1 + 3 1 + 3 2 + 3 3 + . . . + 3 11
= 1 + 3 1 + 3 2 + 3 3 + 3 4 + 3 5 +...+ 3 9 + 3 10 + 3 11
= 1 + 3 1 + 3 2 + 3 3 . 1 + 3 1 + 3 2 + ... + 3 9 1 + 3 1 + 3 2
= 1 + 3 1 + 3 2 . 1 + 3 3 + . . . + 3 9
= 13. 1 + 3 3 + . . . + 3 9 ⋮ 13
b, C = 1 + 3 1 + 3 2 + 3 3 + . . . + 3 11
= 1 + 3 1 + 3 2 + 3 3 + 3 4 + 3 5 + 3 6 + 3 7 + 3 8 + 3 9 + 3 10 + 3 11
= 1 + 3 1 + 3 2 + 3 3 + 3 4 1 + 3 1 + 3 2 + 3 3 + 3 8 1 + 3 1 + 3 2 + 3 3
= 1 + 3 1 + 3 2 + 3 3 . 1 + 3 4 + 3 8
= 40. 1 + 3 4 + 3 8 ⋮ 40
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(C=1+3+3^2+3^3+\cdot\cdot\cdot+3^{11}\)
\(C=\left(1+3+3^2+3^3\right)+\left(3^4+3^5+3^6+3^7\right)+\left(3^8+3^9+3^{10}+3^{11}\right)\)
\(=\left(1+3+3^2+3^3\right)+3^4\left(1+3+3^2+3^3\right)+3^8\left(1+3+3^2+3^3\right)\)
\(=40+3^4\cdot40+3^8\cdot40\)
\(=40\cdot\left(1+3^4+3^8\right)\)
Vì \(40\cdot\left(1+3^4+3^8\right)⋮40\)
nên \(C⋮40\)
#\(Toru\)
\(C=1+3+3^2+3^3+...+3^{11}\)
\(\Rightarrow C=\left(1+3+3^2+3^3\right)+3^4\left(1+3+3^2+3^3\right)+3^8\left(1+3+3^2+3^3\right)\)
\(\Rightarrow C=40+3^4.40+3^8.40\)
\(\Rightarrow C=40\left(1+3^4+3^8\right)⋮40\)
\(\Rightarrow dpcm\)
cho A = 1 + 3 + 32 + 33 + ... + 311
a ) chứng minh A chia hết cho 13
b) chứng minh A chia hết cho 40
![](https://rs.olm.vn/images/avt/0.png?1311)
A=1+3+3^2+3^3+...+3^98+3^99+3^100
A=(1+3+ 3^2)+(3^3+3^4+3^5)+...+(3^98+3^99+3^100)
A=(1+3+3^2)+3^3x(1+3+3^2)+...+3^98x(1+3+3^2)
A=13x3^3x13+...+3^98x13
=> 13x(1+3+3^3+...+3^98)chia hết cho 13
Vậy A chia hết cho 13
![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(A=\left(1+3\right)+...+3^{10}\left(1+3\right)\)
\(=4\left(1+...+3^{10}\right)⋮4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(C=1+3+3^2+...+3^{11}\)
\(=\left(1+3+3^2\right)+...+3^9\left(1+3+3^2\right)\)
\(=13\cdot\left(1+...+3^9\right)⋮13\)
Chứng tỏ rằng C chia hết cho 40