Answers!
Hello Shezad
Depends on the question
Check questions on this page https://www.teachoo.com/2552/1595/Example-3---Let-sequence-be-a1-=-1--an-=-an-1---2/category/Finding-sum-from-series/
and
Comment
There is no as such formula...if you are talking about special series...then first find out it nth term and then do summation of that nth term..refer NCERT for that.
Answer the question...
Hello Shezad
Depends on the question
Check questions on this page https://www.teachoo.com/2552/1595/Example-3---Let-sequence-be-a1-=-1--an-=-an-1---2/category/Finding-sum-from-series/
and
Comment
There is no as such formula...if you are talking about special series...then first find out it nth term and then do summation of that nth term..refer NCERT for that.