How do I show an impulse response leads to a zero-phase frequency response? I'm trying to understand how to show that with real coefficients, the phase response of a filter is 0. Here is the impulse response

$h[n] = b_1d[n+1] + b_0d[n] + b_1d[n-1]$

How should I approach showing this?
1) Define $d[n]$ as a sinusoidal

2) Apply angle addition formulas

3) Simplify

4) Interpret the results

Hope this isn't too much.   Sounds like a homework problem.

Ced