\[1)\ y^{'} = 3\sin x;\]
\[y = 3 \bullet \left( - \cos x \right) + C =\]
\[= - 3\cos x + C.\]
\[2)\ y^{'} = \cos x - \sin x;\]
\[y = \sin x - \left( - \cos x \right) + C =\]
\[= \sin x + \cos x + C.\]
\[3)\ y^{'} = 4x^{3} - 2\cos x;\]
\[y = 4 \bullet \frac{x^{4}}{4} - 2\sin x + C =\]
\[= x^{4} - 2\sin x + C.\]
\[4)\ y^{'} = 3x^{2} - 4e^{2x};\]
\[y = 3 \bullet \frac{x^{3}}{3} - 4 \bullet \frac{1}{2}e^{2x} + C =\]
\[= x^{3} - 2e^{2x} + C.\]