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Which of the following signals is/are periodic?

1. $\mathrm{S}(t)=\cos 2 t+\cos 3 t+\cos 5 t$
2. $\mathrm{S}(t)=\exp (j 8 \pi t)$
3. $S(t)=\exp (-7 t) \sin 10 \pi t$
4. $S(t)=\cos 2 t \cos 4 t$