The signum function is given by $sgn(x)= \begin{cases} \dfrac{x}{ \mid x \mid }; x \neq 0& \\ 0;x=0& \end{cases}$ The Fourier series expansion of $sgn (\cos (t) )$ has
- Only sine terms with all harmonics.
- Only cosine terms with all harmonics.
- Only sine terms with even numbered harmonics.
- Only cosine terms with odd numbered harmonics.