$h[n] = 2( \delta[n-2]-\delta[n-1]-\delta[n-3])$
i computed my frequency response and i have this now: $H[e^{j \omega}] = 2[ e^{-2 j \omega} - e^{-j \omega}-e^{-3 j \omega}]$
$H[e^{j \omega}] = 2[ \cos(2\omega) -i \sin(2\omega)-\cos(\omega)+i\sin(\omega)-\cos(3\omega)+i\sin(3\omega)]$
And i need to compute magnitude and phase. But how can i simplify that? there was a hint given to use trigonometric identities but i can't find some that suit my example.