what is vn method in sequences and series. please explain with 2-3 examples?

this is a method in which we express the nth term of a given serioes as the difference of two consecutive termsof another series and then take out the sum.

for this we have to break the term nth term into two consecutive terms with a negetive sign in between such that putting n+1 in the uth tem or putting n-1 in the nth term would result to another term..

 

it comes only from practice........  

best of luck