`|8x-1|=13-x` , ĐKXĐ:`x≥13`
`<=>`\(\left[ \begin{array}{l}8x-1=13-x\\8x-1=-13+x\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}8x + x =1+13\\8x-x=1-13\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}9x=14\\7x=-12\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=14/9 ( tm ) \\x=-12/7 ( loại ) \end{array} \right.\)
Vậy `S = {14/9}`
