To solve the integral \(\int \frac{\ln ^{2}(3 x)}{5 x} \, dx\), we can use the substitution method. Let \(u = \ln(3x)\), then \(du = \frac{1}{x} dx\). This will simplify the integral into a more manageable form.
Para resolver la integral \(\int \frac{\ln ^{2}(3 x)}{5 x} \, dx\), utilizamos la sustitución \(u = \ln(3x)\). Entonces, \(du = \frac{1}{x} dx\).
Reescribimos la integral en términos de \(u\):
\[
\int \frac{u^2}{5} \, du
\]
Integramos la función simplificada:
\[
\int \frac{u^2}{5} \, du = \frac{1}{5} \int u^2 \, du = \frac{1}{5} \cdot \frac{u^3}{3} = \frac{u^3}{15}
\]
Reemplazamos \(u\) por \(\ln(3x)\):
\[
\frac{(\ln(3x))^3}{15}
\]
\[
\boxed{\frac{(\ln(3x))^3}{15}}
\]