1. The problem statement, all variables and given/known data (Sorry, but I haven't mastered using the sigma notation in these forums yet). Find the sum of the following infinite series: (n=0)^(inf) SIGMA ((pi)cos(n))/(5^n). 2. Relevant equations I tried using the formula S=(a1)/(1-r). I know that a=pi, but I can't find "r." The equation doesn't have a consistent rate. Should I be using a different method? Thanks.