LTI system phase response given $z$-transform I have been given this question


  \begin{equation}
H\left(z\right)\:=\:\frac{1}{6}\left(1+z^{-2}\right)^6
\end{equation}
  
  (a) Compute and plot the phase response of the system.
  
  (b) Determine analytically $\angle H(e^{j\omega})$ and use the formula obtained to compute and plot the phase response.
  
  (c) Compute and plot the phase response using the function freqz.


First of all how to input the expression into MATLAB?
I tried 

Hz1 = [1 0 1];
Hz11 = Hz1.^6


but this does not work. Any clues?
Answer to (b):

$(1+z^{-2})$ is a Type I generalized linear phase filter with group delay 1 (i.e. the phase response is $\angle H(e^{j\theta})=-\theta$ with a jump of $\pi$ at $\theta = \pm \pi/2$).

6 of those filters in cascade will have group delay 6 (phase response $\angle H(e^{j\theta})=-6\theta$).