Question: Simplify

(a) \[\cos 7\omega t\,\cos 3\omega t+\sin 7\omega t\,\sin 3\omega t\]

(b) \[\sin 2\omega t\,\,\cos (2\omega t-k)-\cos 2\omega t\,\,\sin (2\omega t-k)\]

(c) \[-1+{{\cosh }^{2}}A\] (use the exponential representation)

(d) \[\frac{1+\,\sinh \,2A\,+\,\cosh \,2A}{1-\,\sinh \,2A\,-\,\cosh \,2A\,}\]