How does an IIR system affect magnitude and phase of a sinusoidal signal
HINT:


Compute the system's frequency response $$H(e^{j\omega})=\sum_{n=-\infty}^{\infty}h[n]e^{-jn\omega}$$
Compute its magnitude and phase
Figure out (by searching this site or any textbook on Signals and Systems) how the magnitude and phase of $H(e^{j\omega})$ affect a sinusoidal input signal.