Đáp án:

• \(\int \frac{1}{\sin x \cos^3 x} \, dx = \int \frac{1}{\cos^4 x . \tan x} \, dx\)

\(= \int \frac{1}{\cos^2 x} \cdot \frac{1 + \tan^2 x}{\tan x} \, dx\)

\(= \int \frac{1}{\cos^2 x} \cdot \frac{1}{\tan x} \, dx + \int \frac{1}{\cos^2 x} \cdot \tan x \, dx\)

\(= \ln |\tan x| + \frac{\tan^2 x}{2} + C\)