Tìm x: a) x+2/5 = -11/5 b) (c-7/18)*18/29 = -12/29

* Hướng dẫn giải

Lời giải

$$\begin{gathered} \mathit{a}\mathbf{)} x+\frac{2}{5}=\frac{-11}{15} \\ x=\frac{-11}{15}-\frac{2}{5} \\ x=\frac{-13}{15}. \end{gathered}$$

$$\begin{gathered} \mathit{b}\mathbf{)} \left(x-\frac{7}{18}\right).\frac{18}{29}=-\frac{12}{29} \\ x-\frac{7}{18}=-\frac{12}{29}:\frac{18}{29} \\ x-\frac{7}{18}=-\frac{12}{29}.\frac{29}{18} \\ x-\frac{7}{18}=\frac{-2}{3} \\ x=\frac{-2}{3}+\frac{7}{18} \\ x=\frac{-12}{18}+\frac{7}{18} \\ x=\frac{-5}{18}. \end{gathered}$$

$$\begin{gathered} \mathit{c}\mathbf{)} \frac{3}{x+5}=15\% \\ \frac{3}{x+5}=\frac{3}{20} \\ x + 5 = 20 \\ x = 20 – 5 \\ x = 15. \end{gathered}$$