If $y=\frac{\cos x}{1+\sin x}$, then

(a) $\frac{d y}{d x}=\frac{-1}{1+\sin x}$

(b) $\frac{d y}{d x}=\frac{1}{1+\sin x}$

(c) $\frac{\mathrm{dy}}{\mathrm{dx}}=-\frac{1}{2} \sec ^2\left(\frac{\pi}{4}-\frac{\mathrm{x}}{2}\right)$

(d) $\frac{\mathrm{dy}}{\mathrm{dx}}=\frac{1}{2} \sec ^2\left(\frac{\pi}{4}-\frac{\mathrm{x}}{2}\right)$

If $\mathrm{y}=\mathrm{a} \sin ^3 \mathrm{t}, \mathrm{x}=\mathrm{a} \cos ^3 \mathrm{t}$, then $\frac{\mathrm{dy}}{\mathrm{dx}}$ at $\mathrm{t}=\frac{3 \pi}{4}$ is

The derivative of $\sin \mathrm{x}$ with respect to $\log \mathrm{x}$ is