\[\boxed{\mathbf{40}\mathbf{.}}\]
\[\textbf{а)}\ y = x^{- 21};\ \ x \neq 0\]
\[y^{'} = - 21x^{- 22}.\]
\[\textbf{б)}\ y = x^{- 201};\ \ x \neq 0\]
\[y^{'} = - 201x^{- 202}.\]
\[\textbf{в)}\ y = x^{- 2001};\ \ x \neq 0\]
\[y^{'} = - 2001x^{- 2002}\text{.\ }\]