Đáp án:

• \( \int \frac{1}{x(x^4 + 1)} \, dx = \int \frac{1 + x^4 - x^4}{x(x^4 + 1)} \, dx \)

\( = \int \frac{1}{x} \, dx - \int \frac{x^3}{1 + x^4} \, dx \)

\( = \ln|x| - \frac{1}{4} \ln(1 + x^4) + C \)