Cho hàm số

C

- Hướng dẫn giải

Chọn C

$\begin{array}{l}{y}^{\text{'}}=\frac{-\sin x\left(1-\sin x\right)+{\cos }^{2}x}{{\left(1-\sin x\right)}^2}\\ =\frac{-\sin x+\text{}{\sin }^{2}x+{\cos }^{2}x}{{\left(1-\sin x\right)}^2}\\ =\frac{-\mathrm{s}\text{inx}+1}{{(1-\sin x)}^2}=\frac{1}{1-\sin x}\end{array}$

$y^{\text{'}}\left(\frac{\pi }{6}\right)=\frac{1}{1-\sin \frac{\pi }{6}}=2$