# When to use the residue at infinity

1. Mar 15, 2009

### jack5322

why is it that we can use the residue at infinity on the methods of contour integration example on wikipedia for the last one? we can only use the residue at infinity when it is a rational function, i.e. the ratio of two polynomials, if i'm wrong when i say this, why?

2. Mar 25, 2009