\[3x + 2x^{3} + 5x^{5} = 0\]
\[x\left( 3 + 2x^{2} + 5x^{4} \right) = 0\]
\[x = 0;\ \]
\[3 + 2x^{2} + 5x^{4} \neq 0\ при\ любом\ \text{x.}\]
\[Ответ:x = 0.\]