- #1
pivoxa15
- 2,255
- 1
The definition of a residue is the coefficient of the -1 power in the Laruent series. If I do z/cos(z) by long division, I get a series starting with z so z^-1 never occurs hence has a coefficient of 0. But why does it have a non zero residue, namely z/sin(z) at each z when cos(z)=0?