Bài 4:
a: =>-11<x<-8
hay \(x\in\left\{-10;-9\right\}\)
b: =>1<x<4
nên \(x\in\left\{2;3\right\}\)
c: \(\Leftrightarrow\dfrac{9}{21}< \dfrac{x}{21}< \dfrac{14}{21}\)
=>9<x<14
hay \(x\in\left\{10;11;12;13\right\}\)
d: \(\Leftrightarrow\dfrac{-72}{168}< \dfrac{x}{168}< \dfrac{-63}{168}\)
=>-72<x<-63
hay \(x\in\left\{-71;-70;-69;-68;-67;-66;-65;-64\right\}\)