Giải thích các bước giải:
1.$|x-\dfrac{1}{3}|<\dfrac{1}{2}$
$\to -\dfrac{1}{2}<x-\dfrac{1}{3}<\dfrac{1}{2}$
$\to -\dfrac{1}{2}+\dfrac{1}{3}<x<\dfrac{1}{2}+\dfrac{1}{3}$
$\to -\dfrac{1}{6}<x<\dfrac{5}{6}$
2.Ta có :
$a+b=3(b+c)=4(c+a)$
$\to \begin{cases}a+b=3(b+c)\\ 3(b+c)=4(c+a)\end{cases}$
$\to \begin{cases}a=2b+3c\\ 4a=3b-c\end{cases}$
$\to a+2.4a=2b+3c+2(3b-c)\to 9a=8b+c$