Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2004/ib/paper-1/5a/ii/solution

The only pole is the simple one at , with . The point is an essential singularity, not another pole: multiplying by a nonvanishing analytic factor cannot remove its infinite principal part. For completeness its residue can also be read from
The coefficient of is . This extra residue belongs to the essential singularity; it does not change the list of poles.

New to topics? Read the docs here!