Bài 2:
a: Ta có: \(\left|x\right|=\dfrac{12}{31}\)
\(\Leftrightarrow x\in\left\{\dfrac{12}{31};-\dfrac{12}{31}\right\}\)
b: Ta có: \(\left|x\right|=\left|-\dfrac{5}{7}\right|\)
\(\Leftrightarrow\left|x\right|=\dfrac{5}{7}\)
hay \(x\in\left\{\dfrac{5}{7};-\dfrac{5}{7}\right\}\)