Đáp án:
8) \(\left[ \begin{array}{l}
x = \dfrac{1}{5}\\
x = \dfrac{1}{6}
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
1)x = \dfrac{2}{3} - \dfrac{1}{5}\\
\to x = \dfrac{7}{{15}}\\
2)x = \dfrac{4}{9} + \dfrac{5}{8}\\
\to x = \dfrac{{77}}{{72}}\\
3)\dfrac{7}{4}x + \dfrac{3}{2} = - \dfrac{4}{5}\\
\to \dfrac{7}{4}x = - \dfrac{4}{5} - \dfrac{3}{2}\\
\to \dfrac{7}{4}x = - \dfrac{{23}}{{10}}\\
\to x = - \dfrac{{23}}{{10}}:\dfrac{7}{4}\\
\to x = - \dfrac{{46}}{{35}}\\
4)\dfrac{3}{4}x = \dfrac{3}{4} - \dfrac{1}{4}\\
\to \dfrac{3}{4}x = \dfrac{1}{2}\\
\to x = \dfrac{1}{2}:\dfrac{3}{4}\\
\to x = \dfrac{2}{3}\\
5)x.\dfrac{9}{{20}} = \dfrac{{15}}{{56}}\\
\to x = \dfrac{{15}}{{56}}:\dfrac{9}{{20}}\\
\to x = \dfrac{{25}}{{42}}\\
6)\dfrac{3}{{35}} - \dfrac{2}{7} = \dfrac{3}{5} + x\\
\to \dfrac{3}{5} + x = - \dfrac{1}{5}\\
\to x = - \dfrac{4}{5}\\
7)\dfrac{1}{{7x}} = \dfrac{3}{{14}} - \dfrac{3}{7}\left( {x \ne 0} \right)\\
\to \dfrac{1}{{7x}} = - \dfrac{3}{{14}}\\
\to x = \dfrac{1}{7}:\left( { - \dfrac{3}{{14}}} \right)\\
\to x = - \dfrac{2}{3}\\
8)\left[ \begin{array}{l}
5x - 1 = 0\\
2x - \dfrac{1}{3} = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = \dfrac{1}{5}\\
x = \dfrac{1}{6}
\end{array} \right.\\
9) - \dfrac{{15}}{{12}}x - \dfrac{6}{5}x = - \dfrac{1}{2} - \dfrac{3}{7}\\
\to - \dfrac{{49}}{{20}}x = - \dfrac{{13}}{{14}}\\
\to x = \dfrac{{130}}{{343}}
\end{array}\)
