a) x Î Ư(6) = {-6; -3; -2; -l; l; 2; 3; 6}.

b) x + l Î Ư (8) = {- 8; -4; -2; -1; 1; 2; 4; 8}. Từ đó tìm được

x Î{-9; -5; -3; -2; 0; 1; 3; 7}.

c)  x - 2 Î Ư(10) = {-10; -5; - 2; -1; 1; 2; 5; 10). Từ đó tìm được

x Î {-8; -3; 0; l; 3; 5; 7; 12}.

.

1] chứng minh rằng ab - ab chia hết cho 9

Ta có:ab-ab=0\(⋮\)9

2] chứng minh rằng 7 mũ 8+ 7 mũ 7 - 7 mũ 6chia  hết cho 55

Ta có:7⁸+7⁷-7⁶=7⁶.(7²+7-1)=7⁶.55\(⋮\)5

\(\overline{ab}-\overline{ba}\)

\(=\left(10a+b\right)-\left(10b+a\right)\)

\(=9a-9b\)

\(=9\left(a-b\right)⋮9\)

\(7^8+7^7-7^6\)

\(=7^6\cdot\left(7^2+7-1\right)\)

\(=7^6\cdot\left(49+7-1\right)\)

\(=7^6\cdot\left(56-1\right)\)

\(=7^6\cdot55⋮55\)

giúp mình nhé ai làm được thi kb nhé

a) \(6⋮\left(x-1\right)\)

\(\Rightarrow\left(x-1\right)\inƯ\left(6\right)\)

\(Ư\left(6\right)=\left\{1;2;3;6\right\}\)

Có: \(\left(x-1\right)\inƯ\left(6\right)\)

\(\Rightarrow\left(x-1\right)\in\left\{1;2;3;6\right\}\)

\(\Rightarrow x-1=1;x-1=2;x-1=3;x-1=6\)

\(\Leftrightarrow x=2;x=3;x=4;x=7\)

\(\Rightarrow x\in\left\{2;3;4;7\right\}\)

b) \(15⋮\left(2x+1\right)\)

\(\Rightarrow\left(2x+1\right)\inƯ\left(15\right)\)

\(Ư\left(15\right)=\left\{1;3;5;15\right\}\)

Có: \(\left(2x+1\right)\inƯ\left(15\right)\)

\(\Rightarrow\left(2x+1\right)\in\left\{1;3;5;15\right\}\)

\(\Rightarrow2x+1=1;2x+1=3;2x+1=5;2x+1=15\)

\(\Leftrightarrow x\in\varnothing;x=1;x=2;x=7\)

\(\Rightarrow x\in\left\{1;2;7\right\}\)

a,Ta có:3n+24 chia hết cho n-4

=>3n-12+36 chia hết cho n-4

=>3(n-4)+36 chia hết cho n-4

Mà 3(n-4) chia hết cho n-4

=>36 chia hết cho n-4

=>n-4\(\in\)Ư(36)={-36,-18,-12,-9,-6,-4,-3,-2,-1,1,2,3,4,6,9,12,18,36}

=>n\(\in\){-32,-14,-8,-5,-2,0,1,2,3,5,6,7,8,10,13,16,22,40}

n,n-6 chia hết cho n-1

=>n-1-5 chia hết cho n-1

Mà n-1 chia hết cho n-1

=>5 chia hết cho n-1

=>n-1\(\in\)Ư(5)={-5,-1,1,5}

=>n\(\in\){-4,0,2,6}

b)n+6 chia het cho n-1

​=(n-1)+7 chia het cho n-1

​suy ra : 7 chia het cho n-1

​n=7+1

​n=8

a)12-n chia het cho n-1

​=11-(n-1) chia het cho n-1

​suy ra :11 chia het cho n-1

​n=11+1

n=12

trả lời 

n=12

chúc bn 

hc tốt

6 chia hết cho ( x -1) => x-1 là ước của 6 
=> (x-1) € {1 ,2,3,6} 
=> x € {2,3,4,7}

Bài 1 :

a) Ta có :

\(4n-7=4n+12-19=4.\left(n+3\right)-19\)

Ta thấy \(4.\left(n+3\right)⋮n+3\Rightarrow\left(-19\right)⋮n+3\Rightarrow\left(n+3\right)\inƯ\left(-19\right)\)

\(Ư\left(-19\right)=\left\{1;-1;19;-19\right\}\)

Do đó :

\(n+3=1\Rightarrow n=1-3=-2\)

\(n+3=-1\Rightarrow n=-1-3=-4\)

\(n+3=19\Rightarrow n=19-3=16\)

\(n+3=-19\Rightarrow n=-19-3=-22\)

Vậy \(n\in\left\{-2;-4;16;-22\right\}\)

BÀI 2:

a  chia  8  dư   7    \(\Rightarrow\)\(a-7\)\(⋮\)\(8\)\(\Rightarrow\)\(a-7+128\)\(⋮\)\(8\)\(\Rightarrow\)\(a+121\)\(⋮\)\(8\)

a  chia  125  dư  4    \(\Rightarrow\)\(a-4\)\(⋮\)\(125\)\(\Rightarrow\)\(a-4+125\)\(⋮\)\(125\)\(\Rightarrow\)\(a+121\) \(⋮\)\(125\)

suy ra:   \(a+121\)\(\in BC\left(8;125\right)=B\left(1024\right)=\left\{0;1024;2048;3072;...\right\}\)

\(\Rightarrow\)\(a\)\(\in\left\{903;1927;....\right\}\)

mà  \(100< a< 1000\)

\(\Rightarrow\)\(a=903\)