A linear time-invariant system has a transfer function $H(s)=1 /(1+s)$. If the input to the system is $\cos (t)$, the output is
- $\left(e^{j t}+e^{-j t}\right) / 2$ where $j=\sqrt{-1}$
- $\cos (t) / 2$
- $(\cos (t)+\sin (t)) / 2 \sqrt{ }$
- $\sin (t) / 2$.
- The system is unstable and the output is not well-defined.