\(a+2⋮a-1\)
\(=>\left(a-1\right)+3⋮a-1\)
\(\)Vì \(a-1⋮a-1\) mà \(\left(a-1\right)+3⋮a-1\)
\(=>3⋮a-1\)
\(=>a\in\text{Ư}\left(3\right)=\left\{-3;-1;1;3\right\}\)
co a+2=a-1+3
de a+2 chia het cho a-1 thi 3 chia het cho a-1
=> a-1 thuoc uoc cua 3
ma U(3)∈{-1;1;-3;3}
ta co bang sau
| a-1 | -1 | 1 | -3 | 3 |
| a | 0 | 2 | -2 | 4 |
vay...
\(\left(a+2\right)⋮\left(a-1\right)\)
\(\left(a-1+3\right)⋮\left(a-1\right)\)
\(\text{ }\Rightarrow a-1\in\text{Ư}\left(3\right)=\left\{\pm1;\pm3\right\}\)
`+, a-1=1 => a=2`
`+,a-1=-1=>a=0`
`+, a-1=3=>x=4`
`+,a-1=-3=>a=-2`
vậy \(a\in\left\{2;0;4;-2\right\}\)
