Đáp án:
`a, x = 304/15`
`b, x ∈ {-1/2; 1/7}`
Giải thích các bước giải:
$a, 3,8 : 2x= \dfrac{1}{4} : \dfrac{8}{3}\\ ⇒ \dfrac{19}{5} : 2x = \dfrac{1}{4} \times \dfrac{3}{8}\\ ⇒ \dfrac{19}{5} : 2x = \dfrac{3}{32}\\ ⇒ 2x = \dfrac{19}{5} : \dfrac{3}{32}\\ ⇒ 2x = \dfrac{19}{5} \times \dfrac{32}{3}\\ ⇒ 2x = \dfrac{608}{15}\\ ⇒ x = \dfrac{304}{15}\\b, (2x+1)\bigg(x - \dfrac{1}{7} \bigg)=0\\ \Rightarrow \left[ \begin{array}{l}2x + 1 = 0\\x - \dfrac{1}{7}=0\end{array} \right.\\ \Rightarrow \left[ \begin{array}{l}2x=-1\\x= \dfrac{1}{7}\end{array} \right.\\ \Rightarrow \left[ \begin{array}{l}x=\dfrac{-1}{2}\\x=\dfrac{1}{7}\end{array} \right.\\ \text{Vậy x } \{\dfrac{-1}{2}; \dfrac{1}{7}\}$
