\[3x^{2} + 4x = 0\]
\[x(3x + 4) = 0\]
\[x = 0;\ \ \ \ \ 3x + 4 = 0\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 3x = - 4\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = - \frac{4}{3} = - 1\frac{1}{3}\]
\[Ответ:x = - 1\frac{1}{3};\ \ x = 0.\]