1.

`S_(n)` be the sum of n terms of the series `(8)/(5)+(16)/(65)+(24)/(325)+"......"` The seveth term of the series isA. `(56)/(2505)`B. `(56)/(6505)`C. `(56)/(5185)`D. `(107)/(9605)`

Answer» Correct Answer - D
Let `S_n=(8)/(5)+(16)/(65)+(24)/(325)+"......"`
`T_(r)=(8r)/(4r^(4)+1)=(8r)/((2^(2)+2r+1)(2^(2)-2r+1))`
`=2[((2^(2)+2r+1)-(2^(2)-2r+1))/((2^(2)+2r+1)(2^(2)-2r+1))]`
`=2[(1)/((2^(2)-2r+1))-(1)/((2^(2)+2r+1))]`
`T_(7)=(8xx7)/(4xx7^(2)+1)=(56)/(9605)`.


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