Consider the following statements for a system given by $$y\left( n \right) = x\left( n \right)\sum\nolimits_{k = - \infty }^\infty {\delta \left( {n - 3k} \right)} .$$
1. The system is linear.
2. The system is non-linear.
3. The system is causal.
4. The system is non-causal.
Which of the above statements is/are correct?

The Fourier transform of a real valued time signal has

The RMS value of a rectangular wave of period T, having a value of +V for a duration, T₁(< T) and -V for the duration, T - T₁ = T₂ equals

A continuous time function x(t) is periodic with period T. The function is sampled uniformly with a sampling period T_s. In which one of the following cases is the sampled signal periodic?

The phase response of a passband waveform at the receiver is given by
$$\varphi \left( f \right) = - 2\pi \alpha \left( {f - {f_c}} \right) - 2\alpha \beta {f_c},$$
where f_c is the centre frequency, and α and β are positive constants. The actual signal propagation delay from the transmittance to receiver is