Biết

C

- Hướng dẫn giải

Đáp án C

Đặt $\left\{\begin{array}{l}u=\ln \left(x^2+9\right)\\ dv=xdx\end{array}\right.\Rightarrow \left\{\begin{array}{l}du=\frac{2x}{x^2+9}dx\\ v=\frac{x^2+9}{2}\end{array}\right.\Rightarrow \underset{0}{\overset{4}{\int }}x\ln \left(x^2+9\right)dx=\frac{x^2+9}{2}\ln \left(x^2+9\right)\left|{}_0{}^4-\underset{0}{\overset{4}{\int }}xdx\right.$

$=25\ln 5-9\ln 3-8\Rightarrow a=25;b=-9;c=-8\Rightarrow a+b+c=8.$