The Fourier series coefficient of periodic signal \(\rm x\left( t \right)\) is \(\rm {a_k}\). Then, the Fourier series coefficient of. \(\rm x\left( {t - {t_o}} \right) + x\left( {t + {t_o}} \right)\) is :
1
\(\rm 2{a_k}\cos\left( {k{\omega _o}{t_o}} \right)\)
2
\(\rm - 2{a_k}\cos \left( {k{\omega _o}{t_o}} \right)\)
3
\(\rm 2{a_k}\cos\left( {{\omega _o}{t_o}} \right)\)
4
\(\rm - 2{a_k}\cos \left( {{\omega _o}{t_o}} \right)\)