6n+9 chia hết cho 2n-1
ta thấy:
6n+9=(2n-1)x3+12
=>(2n-1)x3 + 12 chia hết cho 2n-1
=>(2n-1)x3 chia hết cho 2n-1
=>12 chia hết cho 2n-1
mã 12 chia hết cho:1;2;3;4;6;12
vậy n=1;2
a, 2n+72n+7⋮n+1
2(n+1)+52(n+1)+5⋮n+1
55⋮n+1hay n+1∈Ư(5)={±1;±5}n+1∈Ư(5)={±1;±5}
b, 4n+94n+9⋮2n+3
2(2n+3)+32(2n+3)+3⋮2n+3
33⋮2n+3hay 2n+3∈Ư(3)={±1;±3}2n+3∈Ư(3)={±1;±3}
2n + 3 | 1 | -1 | 3 | -3 |
2n | -2 | -4 | 0 | -6 |
n | -1 | -2 | 0 | -3 |
n + 1 | 1 | -1 | 5 | -5 |
n | 0 | -2 | 4 | -6 |