Tìm x biết:

\(\frac{1}{3}x + \frac{2}{5}\left( {x + 1} \right) = 0\).

\(\frac{1}{3}x + \frac{2}{5}\left( {x + 1} \right) = 0\)

\( \Leftrightarrow \frac{1}{3}x + \frac{2}{5}x + \frac{2}{5} = 0\)

\( \Leftrightarrow x\left( {\frac{1}{3} + \frac{2}{5}} \right) + \frac{2}{5} = 0\)

\( \Leftrightarrow \frac{{11}}{{15}}x + \frac{2}{5} = 0\)

\( \Leftrightarrow x = \frac{{ - 6}}{{11}}\).

Vậy \(x = \frac{{ - 6}}{{11}}\).