Giả sử \(\int\limits_0^2 {\...

B

- Hướng dẫn giải

$\begin{array}{l}\int\limits_0^2 {\frac{{x - 1}}{{{x^2} + 4x + 3}}dx = \int\limits_0^2 {\left( {\frac{2}{{x + 3}} - \frac{1}{{x + 1}}} \right)dx = \left( {2\ln \left| {x + 3} \right| - \ln \left| {x + 1} \right|} \right)\left| \begin{array}{l}^2\\_0\end{array} \right. = 2\ln 5 - 3\ln 3} } \\ \Rightarrow \left\{ \begin{array}{l}a = 2\\b = - 3\end{array} \right. \Rightarrow ab = - 6\end{array}$