1.

If sum of x terms of a series is `S_(x)=(1)/((2x+3)(2x+1))` whose `r^(th)` term is `T_(r)`. Then, `sum_(r=1)^(n) (1)/(T_(r))` is equal toA. `(1)/(4)sum(2r+1)(2r-1)(2r+3)`B. `-(1)/(4)sum(2r+1)(2r-1)(2r+3)`C. `sum(2r+1)(2r-1)(2r+3)`D. none of these

Answer» Correct Answer - B
we have, `S_(x)=(1)/((2x+3)(2x+1))`
`:." "T_(x)=S_(x)-S_(x-1)`
`rArr" "T_(x)=(1)/((2x+3)(2x+1))-(1)/((2x+1)(2x-1))`
`rArr" "(-4)/((2x-1)(2x+1)(2x+3))`
`:." "underset(r=1)overset(n)sum(1)/(T_(r))=-(1)/(4)underset(r=1)overset(n)sum(2r-1)(2r+1)(2r+3)`


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