A=3^1+3^2+3^3+...+3^29+3^30 chứng minh rằng A chia hết cho 13
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\(A=3+3^2+3^3+...+3^{28}+3^{29}+3^{30}\)
\(A=\left(3+3^2\right)+\left(3^3+3^4\right)+...+\left(3^{29}+3^{30}\right)\)
\(A=1\left(3+3^2\right)+3^2\left(3+3^2\right)+....+3^{28}\left(3+3^2\right)\)
\(A=\left(1+3^2+...+3^{28}\right)\left(3+3^2\right)\)
\(A=13\left(1+3^2+...+3^{28}\right)⋮13\left(đpcm\right)\)
TA CÓ:
A=30+3+32+33+........+311
(30+3+32+33)+....+(38+39+310+311)
3(0+1+3+32)+......+38(0+1+3+32)
3.13+....+38.13 cHIA HẾT CHO 13 NÊN A CHIA HẾT CHO 13( đpcm)
a)\(2^{29}+2^{30}=2^{29}\left(1+2\right)=2^{29}.3⋮3\)
Vậy \(2^{29}+2^{30}⋮3\)
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Câu 2:
\(C=3^{10}+3^{11}+3^{12}+...+3^{17}.\)
\(C=\left(3^{10}+3^{11}+3^{12}+3^{13}\right)+\left(3^{14}+3^{15}+3^{16}+3^{17}\right).\)
\(C=3^{10}\left(1+3+3^2+3^3\right)+3^{14}\left(1+3+3^2+3^3\right).\)
\(C=3^{10}\left(1+3+9+27\right)+3^{14}\left(1+3+9+27\right).\)
\(C=3^{10}.40+3^{14}.40.\)
\(C=\left(3^{10}+3^{14}\right).40⋮40\left(đpcm\right).\)
\(C=3^{10}+3^{11}+..+3^{17}\\ =\left(3^{10}+3^{11}+3^{12}+3^{13}\right)+\left(3^{14}+..+3^{17}\right)\\ =3^{10}\left(1+3+3^2+3^3\right)+3^{14}\left(1+3+3^2+3^3\right)\\ =40\left(3^{10}+3^{14}\right)⋮40\)
ta có: A = 1 + 3 + 32 +...+ 329 ( có 30 chữ số)
A = (1+3+32) + ...+ (327+328+329) ( có 10 cặp)
A = 13 + ...+ 327.(1+3+32)
A = 13.(1+...+ 327) chia hết cho 13
a) (1+5+52+53+...529)chia hết cho 6
Đặt (1+5+52+53+...529) = A
\(A=\left(1+5\right)+\left(5^2+5^3\right)+\left(5^4+5^5\right)....+\left(5^{28}+5^{29}\right)\)
\(A=\left(1+5\right)+5^2\left(5+1\right)+5^4\left(5+1\right)+...+5^{28}\left(5+1\right)\)
\(A=6+5^2.6+5^4.6+...+5^{28}.6\)
Vậy A chia hết cho 6
b) (1+3+3^2+3^3+...+3^29) chia hết cho 13
Đặt B= (1+3+3^2+3^3+...+3^29)
\(B=\left(1+3+3^2\right)+\left(3^3+3^4+3^5\right)+...+\left(3^{27}+3^{28}+3^{29}\right)\)
\(B=13+3^3\left(1+3+3^2\right)+....+3^{27}\left(1+3+3^2\right)\)
\(B=13+3^3.13+....+3^{27}.13\)
Vậy B chia hết 13
Câu c,d tương tự.Chúc bạn học tốt

ghép 3 số vào thì ra 1 số chia hết cho 13
sau đó ta phân tích ra giống như tổng ban đầu rồi dùng tính chất phân phối rồi sẽ ra 1 tích cos 13
A=(3^1+3^2+3^3)+(3^4+3^5+3^6)+.........+(3^28+3^29+3^30)(có 10 nhóm)
=(3^1+3^2+3^3)+3^3x(3^1+3^2+3^3)+..............+3^27x(3^1+3^2+3^3)
=(3^1+3^2+3^3)x(1+3^3+...........+3^27)
=39x(1+3^3+...........+3^27)
=13x3x(1+3^3+...........+3^27) chia hết cho 13 (đccm)
tick nha