Bảng xét dấu :
$\begin{array}{|c|c|}\hline x&-5&3\\\hline x-3&-&+-0+\\\hline x+5&-0-&+\\\hline\end{array}$
TH1 :
`x < -5`
`⇔ 3 - x - (x+5) = 8`
`⇔ 3-x-x-5=8`
`⇔ -2x = 10`
`⇔ x = -5\text{(loại)}`
TH2 :
`-5 \le x < 3`
`⇔ 3 - x + x + 5 = 8`
`⇔ 8 = 8\text{(đúng)}`
TH3 :
`x \ge 3`
`⇔ x - 3 + x + 5 = 8`
`⇔ 2x = 6`
`⇔ x = 3(TM)`
Vậy `S = {x ∈ R | - 5 \le x \le 3}`