Đáp án:
Giải thích các bước giải:
$a) |x+2,8|=3,5$
$⇔\left[ \begin{array}{1}x+2,8=3,5\\x+2,8=-3,5\end{array} \right.$
$⇔\left[ \begin{array}{1}x=0,7\\x=-6,3\end{array} \right.$
Vậy $x∈\{0,7 ; -6,3\}$
$b,\left |x+\dfrac{1}{4} \right |-\dfrac{1}{3}=\dfrac{5}{6}$
$⇔\left |x+\dfrac{1}{4} \right |=\dfrac{5}{6}+\dfrac{1}{3}$
$⇔\left |x+\dfrac{1}{4} \right |=\dfrac{7}{6}$
$⇔\left[ \begin{array}{1}x+\dfrac{1}{4}=\dfrac{7}{6}\\x+\dfrac{1}{4}=-\dfrac{7}{6}\end{array} \right.$
$⇔\left[ \begin{array}{1}x=\dfrac{11}{12}\\x=-\dfrac{17}{12}\end{array} \right.$
Vậy $x∈\left \{\dfrac{11}{12} ; -\dfrac{17}{12} \right \}$
