\(\boxed{\mathbf{41}\mathbf{.}}\)
\[\textbf{а)}\ y = \frac{1}{x^{21}} = x^{- 21};\ \ x \neq 0\]
\[y^{'}(x) = - 21x^{- 22}.\]
\[\textbf{б)}\ y = \frac{2}{x^{25}} = 2x^{- 25};\ \ x \neq 0\]
\[y^{'} = 2 \cdot ( - 25)x^{- 26} = - 50x^{- 26}.\]
\[\textbf{в)}\ y = - \frac{5}{x^{20}} = - 5x^{- 20};\ \ x \neq 0\]
\[y^{'} = - 5 \cdot ( - 20)x^{- 21} = 100x^{- 21}\text{.\ }\]