1. The problem statement, all variables and given/known data 1/(1-cos(z)) 2. Relevant equations taylor expansion at 0 for cos(z)=1-x^2/2+x^4/24 and so on. 1/(x^2/2+x^4/24.......) 3. The attempt at a solution Because all of the powers are negative wouldn't that make it a essential singularity and 0 + 2∏n. Also it just explodes at those points.