Đáp án:
`↓↓ `
Giải thích các bước giải:
`a) A in Z <=> (3n+7)/(n-2) in Z`
`<=> 3n+7 vdots n-2`
`=> 3(n-2)+9 vdots n-2`
Mà `3(n-2) vdots n-2`
`=> 9 vdots n-2`
`=> n-1 in Ư(9)={-9;-3;-1;1;3;9}`
`=> n in {-8;-2;0;2;4;10}`
`b) B in Z <=> (4n-5)/(2n-1) in Z`
`<=> 4n-5 vdots 2n-1`
`<=> 2(2n-1)-3vdots 2n-1`
Mà `2(2n-1) vdots 2n-1`
`=> 3 vdots 2n-1`
`=> 2n-1 in Ư(3)={-3; -1; 1; 3}`
`=> 2n in {-2; 0; 2; 4}`
`=> n in {-1; 0; 1; 2}`
`c) C in Z <=> (n-3)/(n+5) in Z`
`<=> n-3 vdots n+5`
`<=> n+5-8 vdots n+5`
Mà `n+5 vdots n+5`
`=> 8 vdots n+5`
`=> n+5 in Ư(8)={-8;-4;-2;-1;1;2;4;8}`
`=> n in {-13;-9;-7;-6;-4;-3;-1;3}`
