Ta có : `(-8)/13 + 7/17 + 21/13 ≤ x ≤ (-9)/14 + 3 + 5/-14`
`⇔ ( (-8)/13 + 21/13 ) + 7/17 ≤ x ≤ ( (-9)/14 + (-5)/14 ) + 3`
`⇔ 1 + 7/17 ≤ x ≤ -1 + 3`
`⇔ 24/17 ≤ x ≤ 2`
`⇔ 24/17 ≤ x ≤ 34/17`
`⇔ x ∈ { 24/17 ; 25/17 ; 26/17 ; .... ; 34/17 }`
Vậy , `x ∈ { 24/17 ; 25/17 ; 26/17 ; .... ; 34/17 }`