Cho hàm số

B

- Hướng dẫn giải

Đáp án B

$\begin{array}{l}f\text{'}\left(x\right)=3{\sin }^{2}x.c\text{osx + 2x}\\ {\text{ f\hspace{0.17em}"(x) = 3.2sinx.cosx. cosx+ 3sin}}^{2}x.(-\sin x)+\text{}2\\ =6\sin x.c{\text{os}}^2{\text{x - 3sin}}^{3}x+\text{}2\\ \Rightarrow f"\left(\frac{\pi }{2}\right)=\mathrm{6.1.0}-{3.1}^3+\text{\hspace{0.17em}}2=-1\end{array}$