Como quieres eliminar f = 60Hz,
$$ \ mid H (e ^ {jw}) \ mid = 0 $$ para $$ w = 2 \ pi * 60 rad $$
$$ \ frac {\ mid (1-e ^ {- j (w-w_ {0})}) (1-e ^ {- j (w + w_ {0})}) \ mid} { \ mid (1-0.9e ^ {- j (w-w_ {0})}) (1-0.9e ^ {- j (w + w_ {0})}) \ mid} = 0 $$
$$ \ mid (1-e ^ {- j (w-w_ {0})}) (1-e ^ {- j (w + w_ {0})}) \ mid = 0 $$
$$ {\ mid1- e ^ {- j (w-w_ {0})} - e ^ {- j (w + w_ {0})} + e ^ {- j2w} \ mid} = 0 $$
$$ {\ mid1- e ^ {- jw} (e ^ {jw_ {0}} + e ^ {- jw_ {0}}) + e ^ {- j2w} \ mid} = 0 $$
$$ {\ mid1- 2e ^ {- jw} cos (w_ {0}) + e ^ {- j2w} \ mid} = 0 $$
ahora $$ w = 2 \ pi * 60, e ^ {- jw} = 1 $$
Por lo tanto,
$$ \ mid2-2cos (w_ {0}) \ mid = 0 $$
$$ cos (w_ {0}) = 1 $$
Determine w0 por usted mismo