catch_arnie is correct, such problems are done thru Vn method (as i normally call it)
basically the thing to be done here is, write the rth term of the given series...
then if the series is in the product form , write a term Vr, containing one term more than the given ones, like if the Tr contains 4 terms, then Vr will contain 5 terms....
and if its of quotient form [like 1/ (1.2.3) + 1/(2.3.4)+....], then Vr will contain a term less than Tr, [if Tr =1/ (n+r) (n+r+1)(n+r+2), then Vr =1/ (n+r+1)(n+r+2) ]
in both the cases, on taking difference of Vr and V(r-1), u'll get Tr
and thus on summation it will be left with only two terms.... which can easily be calculated.....
any confusion, do ask again
Moderation Team
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