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b: \(B=16^5+2^{15}\)
\(=\left(2^4\right)^5+2^{15}\)
\(=2^{20}+2^{15}\)
\(=2^{15}\left(2^5+1\right)=2^{15}\cdot33⋮33\)
c: \(45⋮9;99⋮9;180⋮9\)
Do đó: \(45+99+180⋮9\)
=>\(C⋮9\)
d: \(D=2+2^2+2^3+...+2^{60}\)
\(=\left(2+2^2+2^3\right)+\left(2^4+2^5+2^6\right)+...+\left(2^{58}+2^{59}+2^{60}\right)\)
\(=2\left(1+2+2^2\right)+2^4\cdot\left(1+2+2^2\right)+...+2^{58}\left(1+2+2^2\right)\)
\(=7\left(2+2^4+...+2^{58}\right)⋮7\)
\(D=2+2^2+2^3+...+2^{60}\)
\(=\left(2+2^2+2^3+2^4\right)+\left(2^5+2^6+2^7+2^8\right)+...+\left(2^{57}+2^{58}+2^{59}+2^{60}\right)\)
\(=2\left(1+2+2^2+2^3\right)+2^5\left(1+2+2^2+2^3\right)+...+2^{57}\left(1+2+2^2+2^3\right)\)
\(=15\left(2+2^5+...+2^{57}\right)\)
=>D chia hết cho cả 3 và 5
a) \(7^6+7^5-7^4=7^4\left(7^2+7-1\right)=7^4\left(49+7-1\right)=7^4.55⋮55\)
b) \(16^5+2^{15}=\left(2^4\right)^5+2^{15}=2^{20}+2^{15}=2^{15}\left(2^5+1\right)=2^{15}\left(32+1\right)=2^{15}.33⋮33\)
c) \(81^7-27^9-9^{13}=\left(3^4\right)^7-\left(3^3\right)^9-\left(3^2\right)^{13}=3^{28}-3^{27}-3^{26}=3^{26}\left(3^2-3-1\right)=3^{26}.5=3^{22}.3^4.5=3^{22}.405⋮405\)
a: \(=7^4\left(7^2+7-1\right)=7^4\cdot55⋮55\)
b: \(=2^{20}+2^{15}=2^{15}\left(2^5+1\right)=2^{15}\cdot33⋮33\)
c: \(=3^{28}-3^{27}-3^{26}=3^{26}\left(3^2-3-1\right)=3^{26}\cdot5=3^{22}\cdot405⋮405\)
a: \(A=\left(1+3\right)+...+3^{10}\left(1+3\right)\)
\(=4\left(1+...+3^{10}\right)⋮4\)
a) A = 1 + 3 + 32 + .... + 311
= (1+3+32 ) + ( 33 + 34 + 35) + ..... + (39 + 310 + 311)
= 13 + 33 . 13 + .... + 39 . 13
= 13 . (1+ 33 +....+ 39)
=> A chia hết cho 13
b) B = 165 + 215
= 220 +215
= 215 . 25 + 215
= 215 . ( 25 + 1)
= 215 .33
=> B chia hết cho 33
c) C= 5 + 52 + 53 + .....+ 58
= (5 + 52) + (53 + 54) +....+ ( 57 + 58)
= 30 + 52 (5 + 52) + ....+ 56 ( 5 + 52)
= 30 + 52 . 30 + .....+ 56 . 30
= 30. ( 1+ 52 +....+ 56 )
=> C chia hết cho 30
d) D= 45 + 99+ 180 chia hết cho 9
Do 45 chia hết cho 9
99 chia hết cho 9
180 chia hết cho 9
=> 45 + 99 + 180 chia hết cho 9
e) E = 1+ 3 + 32 + 33 + ......+ 3199
= (1+3+32) + (33 + 34 + 35) +......+ (3197 + 3198 + 3199)
= 13 + 33 (1+3+32) +.......+ 3197(1+3+32)
= 13 + 33 . 13 + ..... + 3197 .13
= 13. ( 1+ 33 +....+ 3197)
=> E chia hết cho 13
f)
Ta có: 1028 + 8 = 100...08 (27 chữ số 0)
Xét 008 chia hết cho 8 => 1028 + 8 chia hết cho 8 (1)
Mà 1+27.0+ 8 = 9 chia hết cho 9 => 1028 + 8 chia hết cho 9 (2)
Mà (8,9) =1 (3)
Từ (1); (2); (3) => 1028 + 8 chia hết cho (8.9)= 72
g)
ta có: G= 88 + 220 = (23)8 + 220 = 224 + 220 = 220 . 24 + 220 = 220 . (24 + 1) = 220 . 17
=> G chia hết cho 17
a) A = 1 + 3 + 3^2 + ... + 3^11
A = ( 1 + 3 + 3^2 ) + ... + ( 3^9 + 3^10 + 3^11 )
A = 1(1 + 3 + 3^2 ) + ... + 3^9 ( 1 + 3 + 3^2 )
A = 1 . 13 + ... + 3^9 . 13
A = 13 ( 1 + ... + 3^9 ) chia hết cho 13
còn mấy ý kia bạn chỉ cần tách nhóm rồi làm tương tự là ok
Good luck
\(C=1+3+3^2+3^3+...+3^{11}\\ a,C=\left(1+3+3^2\right)+\left(3^3+3^4+3^5\right)+\left(3^6+3^7+3^8\right)+\left(3^9+3^{10}+3^{11}\right)\\ =13+3^3.\left(1+3+3^2\right)+3^6.\left(1+3+3^2\right)+3^9.\left(1+3+3^2\right)\\ =13+3^3.13+3^6.13+3^9.13\\ =13.\left(1+3^3+3^6+3^9\right)⋮13\)
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
cho C=5+52+53+54+...+520 chứng minh rằng:
a)C chia hết cho 5 b) C chia hết cho 6 c) C chia hết cho 13
\(a,C=5+5^2+5^3+5^4+\cdot\cdot\cdot+5^{20}\)
\(=5\left(1+5+5^2+\cdot\cdot\cdot+5^{19}\right)\)
Ta thấy: \(5\left(1+5+5^2+\cdot\cdot\cdot+5^{19}\right)⋮5\)
nên \(C⋮5\)
\(b,C=5+5^2+5^3+5^4\cdot\cdot\cdot+5^{20}\)
\(=\left(5+5^2\right)+\left(5^3+5^4\right)+\cdot\cdot\cdot+\left(5^{19}+5^{20}\right)\)
\(=5\left(1+5\right)+5^3\left(1+5\right)+\cdot\cdot\cdot+5^{19}\left(1+5\right)\)
\(=5\cdot6+5^3\cdot6+\cdot\cdot\cdot+5^{19}\cdot6\)
\(=6\cdot\left(5+5^3+\cdot\cdot\cdot+5^{19}\right)\)
Ta thấy: \(6\cdot\left(5+5^3+\cdot\cdot\cdot+5^{19}\right)⋮6\)
nên \(C⋮6\)
\(c,C=5+5^2+5^3+5^4+\cdot\cdot\cdot+5^{20}\)
\(=\left(5+5^3\right)+\left(5^2+5^4\right)+\cdot\cdot\cdot+\left(5^{17}+5^{19}\right)+\left(5^{18}+5^{20}\right)\)
\(=5\left(1+5^2\right)+5^2\left(1+5^2\right)+\cdot\cdot\cdot+5^{17}\cdot\left(1+5^2\right)+5^{18}\left(1+5^2\right)\)
\(=5\cdot26+5^2\cdot26+\cdot\cdot\cdot+5^{17}\cdot26+5^{18}\cdot26\)
\(=26\cdot\left(5+5^2+\cdot\cdot\cdot+5^{17}+5^{18}\right)\)
Ta thấy: \(26\cdot\left(5+5^2+\cdot\cdot\cdot+5^{17}+5^{18}\right)⋮13\)
nên \(C⋮13\)
#\(Toru\)
C = 5 + 5^2 + 5^3 + 5^4 + ... + 5^20
=> C = 5 . ( 1 + 5 + 5^2 + 5^3 + ... + 5^19 )
=> C chia hết cho 5
b,
C = 5 + 5^2 + 5^3 + 5^4 + ... + 5^20
=> C = 5 . ( 1 + 5 ) + 5^3 . ( 1 + 5 ) + ... + 5^19 . ( 1 + 5 )
=> C = 5 . 6 + 5^3 . 6 + ... + 5^19 . 6
=> C = 6 . ( 5 + 5^3 + ... + 5^19 )
=> C chia hết cho 6
c,
C = 5 + 5^2 + 5^3 + ... + 5^20
=> C = (5 + 5^2 + 5^3 + 5^4 ) + ... + (5^17 + 5^18 + 5^19 + 5^20 )
=> C = 5 . ( 1 + 5 + 5^2 + 5^3 ) + ... + 5^17 . ( 1+ 5 + 5^2 +5^3)
=> C = 5 . 156 + 5^5 . 156 + ...+ 5^17 . 156
=> C = 5 . 12 . 13 + 5^5 . 12 . 13 + ... + 5^17 . 12 . 13
=> C = 13 . ( 5 . 12 + 5^5 . 12 + ... + 5^17 . 12 )
=> C chia hết cho 13
Bài 1:
\(a,A=\left(2+2^2\right)+\left(2^3+2^4\right)+...+\left(2^{2009}+2^{2010}\right)\\ A=\left(1+2\right)\left(2+2^3+...+2^{2009}\right)=3\left(2+...+2^{2009}\right)⋮3\\ A=\left(2+2^2+2^3\right)+...+\left(2^{2008}+2^{2009}+2^{2010}\right)\\ A=\left(1+2+2^2\right)\left(2+...+2^{2008}\right)=7\left(2+...+2^{2008}\right)⋮7\)
\(b,\left(\text{sửa lại đề}\right)B=\left(3+3^2\right)+\left(3^3+3^4\right)+...+\left(3^{2009}+3^{2010}\right)\\ B=\left(1+3\right)\left(3+3^3+...+3^{2009}\right)=4\left(3+3^3+...+3^{2009}\right)⋮4\\ B=\left(3+3^2+3^3\right)+...+\left(3^{2008}+3^{2009}+3^{2010}\right)\\ B=\left(1+3+3^2\right)\left(3+...+3^{2008}\right)=13\left(3+...+3^{2008}\right)⋮13\)
Bài 2:
\(a,\Rightarrow2A=2+2^2+...+2^{2012}\\ \Rightarrow2A-A=2+2^2+...+2^{2012}-1-2-2^2-...-2^{2011}\\ \Rightarrow A=2^{2012}-1>2^{2011}-1=B\\ b,A=\left(2020-1\right)\left(2020+1\right)=2020^2-2020+2020-1=2020^2-1< B\)
bt àm câu a thôi '
7a5b1 \(⋮3\Leftrightarrow\left(7+a+5+b+1\right)⋮3\Leftrightarrow\left(13+a+b\right)⋮3\)
\(\Rightarrow a+b\in\left\{2,5,8,11,14,17\right\}\)
Vì a-b=4 là chẵn\(\Rightarrow a+b\)và
a+b > 4 nên \(a+b\in\left\{8,14\right\}\)
+Nếu a+b=8 a-b=4
thì a=6
b=2
+Nếu a+b=14 a-b=4
thì a=9
b=5
Vậy a=6 và b=2
a=9 và b=5
c) C = 5 + 52 + 53 +...+ 58
= ( 5 + 52 ) + ( 53 + 54 ) + ( 55 + 56 ) + ( 57 + 58 )
= 5 + 52 + 52( 5 + 52 ) + 54( 5 + 52 ) + 56( 5 + 52 )
= 5 + 52 ( 1 + 52 + 54 + 56 )
= 30. ( 1 + 52 + 54 + 56 ) chia hết cho 30
Vậy C = 5 + 52 + 53 +...+ 58 chia hết cho 30
b) B = 165 + 215
= (24)5 + 215
= 220 + 215
= 215. 25 + 215
= 215(25 + 1)
= 215.33 chia hết cho 33
Vậy B = 165 + 215 chia hết cho 33