Biết rằng

A

- Hướng dẫn giải

Đáp án A

Ta có:

$$\begin{gathered} \underset{1}{\overset{2}{\int }}\ln \left(x+1\right)dx=\underset{1}{\overset{2}{\int }}\ln \left(x+1\right)d\left(x+1\right) \\ ={\left.\left(x+1\right)\ln \left(x+1\right)\right|}_1^2-\underset{1}{\overset{2}{\int }}\left(x+1\right)d\left(\ln \left(x+1\right)\right) \\ =3\ln 3-2\ln 2-\underset{1}{\overset{2}{\int }}dx=3\ln 3-2\ln 2-1 \\ \Rightarrow a=3;b=-2;c=-1\Rightarrow a+b+c=0. \end{gathered}$$