Đặt \(t=x+\sqrt{x^{2} -3} \Rightarrow {\rm d}t=\left(1+\frac{x}{\sqrt{x^{2} -3} } \right){\rm d}x\) hay \(\frac{{\rm d}x}{\sqrt{x^{2} -3} } =\frac{{\rm d}t}{t} .\)
\(\int \frac{{\rm d}x}{\sqrt{x^{2} -3} } =\int \frac{{\rm d}t}{t} =\ln \left|t\right|+C=\ln \left|x+\sqrt{x^{2} -3} \right|+C.\)