Đáp án:

• \( \int \frac{1}{x^2 + 4} \, dx = \frac{1}{4} \int \frac{1}{1 + \left( \frac{x}{2} \right)^2} \, dx = \frac{1}{2} \int \frac{\frac{1}{2}}{1 + \left( \frac{x}{2} \right)^2} \, dx \)

\( = \frac{1}{2} \arctan \left( \frac{x}{2} \right) + C \)