The derivative of

$$ y=(1-x)(2-x) \ldots \ldots \ldots \ldots \ldots \ldots(\mathrm{n}-x) $$

at $x=1$ is

The first derivative of the function $\left(\cos ^{-1}\left(\sin \sqrt{\frac{1+x}{2}}\right)+x^x\right)$ with respect to $x$ at $x=1$ is

If $x^{\frac{2}{5}}+y^{\frac{2}{5}}=\mathrm{a}^{\frac{2}{5}}$ then $\frac{\mathrm{d} y}{\mathrm{~d} x}=$