$a$) `x - 1/9 = 8/3`
`⇔ x = 24/9 + 1/9`
`⇔ x = 25/9`
Vì $x ∈ Z ⇒ x ∈ \varnothing$
Vậy $ x ∈ \varnothing$.
$b$) `- x/4 = - 9/x`
`⇔ x^2 = 36`
`⇔ x ∈ {±6}`
Vậy `x ∈ {±6}`.
$c$) `x/4 = {18}/{x+1}`
`⇔ x.(x+1) = 72`
`⇒` \(\left[ \begin{array}{l}x=8\\x=-9\end{array} \right.\)
Vậy `x` $∈$ `{8;-9}`.