`a, A = [2/[3x] - 2/[x+1] ( [x+1]/[3x] - x - 1)] : [x-1]/x ( x ne 0 ; 1 ; - 1)`

`= [ 2/[3x] - 2/[x+1] . [x+1 - 3x(x+1)]/[3x] ] . x/[x-1]`

`= [2/[3x] - 2/[x+1] . [-3x^2 - 2x + 1]/[3x] ]. x/[x-1]`

`= [2/[3x] + 2/[x+1] . [(3x-1)(x+1)]/[3x] ] . x/[x-1]`

`= [2/[3x] + [6x - 2]/[3x] ] . x/[x-1]`

`= [6x]/[3x] . x/[x-1]`

`= [2x]/[x-1]`

`b, A = [2(x-1) + 2]/[x-1] = 2+  2/[x-1]`

`A in ZZ`

`=> x-  1 in {-2;-1;1;2}`

`=> x in {-1;0;2;3}`

Kết hợp điều kiện `-> x in {2;3}`