I need help with 11c and 13 a I'll try to do 13 b if I get 13a

[reef plaza]

11c is standard results

13a is a telescoping series

basically means a lot will cancel out

so if u list the first few terms of it

1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5

you can see lots cancels