Determine the Fourier-series expansion of the following signals: \text { 1. } x(t)=\cos (2 \pi t)+\cos (4 \pi t) \text { 2. } x(t)=\cos (2 \pi t)-\cos (4 \pi t+\pi

/ 3) \text { 3. } x(t)=2 \cos (2 \pi t)-\sin (4 \pi t) \text { 4. } x(t)=\sum_{n=-\infty}^{\infty} \Lambda(t-2 n)