/ 2 \ | z | lim |-----------| z->2*pi*n+\-1 + cos(z)/
Limit(z^2/(-1 + cos(z)), z, (2*pi)*n)
/ 2 \ | z | lim |-----------| z->2*pi*n+\-1 + cos(z)/
2 2 4*pi *n ---------------- -1 + cos(2*pi*n)
/ 2 \ | z | lim |-----------| z->2*pi*n-\-1 + cos(z)/
2 2 4*pi *n ---------------- -1 + cos(2*pi*n)
4*pi^2*n^2/(-1 + cos(2*pi*n))
2 2 4*pi *n ---------------- -1 + cos(2*pi*n)