\[\boxed{\mathbf{996}\mathbf{.}}\]
\[1)\ f(x) = \sin x \bullet \cos x = \frac{1}{2}\sin{2x};\]
\[F(x) = \frac{1}{2} \bullet \left( - \frac{1}{2} \right) \bullet \cos{2x} =\]
\[= - \frac{1}{4}\cos{2x} + C.\]
\[2)\ f(x) =\]
\[= \sin x \bullet \cos{3x} - \cos x \bullet \sin{3x} =\]
\[= \sin(x - 3x) = - \sin{2x};\]
\[F(x) = - 1 \bullet \left( - \frac{1}{2} \right) \bullet \cos{2x} =\]
\[= \frac{1}{2}\cos{2x}.\]