\[\boxed{\mathbf{68}\mathbf{.}}\]
\[\textbf{а)}\ f(x) = \sin x\]
\[f^{'}(x) = \cos x;\]
\[f^{''}(x) = - \sin x;\]
\[f^{'''}(x) = - \cos x;\]
\[f^{(4)}(x) = \sin x;\]
\[f^{(5)}(x) = \cos x;\]
\[f^{(6)}(x) = - \sin x;\]
\[f^{(7)}(x) = - \cos x;\]
\[f^{(8)}(x) = f^{(4)} = \sin x.\]
\[Получаем\ для\ любого\ n \in N:\]
\[f^{(4n - 3)}(x) = \cos{x;}\]
\[f^{(4n - 2)}(x) = - \sin x;\]
\[f^{(4n - 1)}(x) = - \cos x;\]
\[f^{(4n)}(x) = \sin x.\]
\[200 = 4 \cdot 50:\]
\[f^{(200)}(x) = \sin x.\]
\[\textbf{б)}\ f(x) = \cos x;\]
\[f^{'}(x) = - \sin x;\]
\[f^{''}(x) = - \cos x;\]
\[f^{'''}(x) = \sin x;\]
\[f^{(4)}(x) = \cos x;\]
\[f^{(5)}(x) = - \sin x;\]
\[f^{(6)}(x) = - \cos x;\]
\[f^{(7)}(x) = \sin x;\]
\[f^{(8)}(x) = f^{(4)} = \cos x.\]
\[Получаем\ для\ любого\ n \in N:\]
\[f^{(4n - 3)}(x) = - \sin x\]
\[f^{(4n - 2)}(x) = - \cos x;\]
\[f^{(4n - 1)}(x) = \sin x;\]
\[f^{(4n)}(x) = \cos x.\]
\[200 = 4 \cdot 50:\]
\[f^{(200)}(x) = \cos x.\]
\[\textbf{в)}\ f(x) = e^{x};\]
\[f^{'}(x) = e^{x};\]
\[f^{(200)} = e^{x}.\]