Find the infinite sum of 1/7+2/7^2+1/7^3+2/7^4...

ok, now I know. its the sum of 2 geometric series: (1/7+1/7^3+1/7^5...) + (2/7^2+2/7^4+2/7^6...)

the first part is equal to 7/48, the second part is equal to 2/48, and they add to 9/48, which is 3/16.

yayy

argh, still don't know how to do this!