If S(n) denotes the sum of first n natural numbers.the [S_(1)+S_(2)x+S_(3)x^(2)+........+S_(n)*x^(n-1)+..],[" ,then n is

If S_(n) denotes the sum of first 'n' natural numbers then S_(1)+S_(2)x+S_(3)x^(2)+........+S_(n)*x^(n-1)+.. then n is

If S_(n) denotes the sum of first 'n' natural numbers then S_(1)+S_(2)x+S_(3)x^(2)+........+S_(n)*x^(n-1)+.....oo= then n is

If S_(n) denotes the sum of first n naturalnumbers, then S_(1)+S_(2)x+S_(3)x^(2)+.......+S_(n)x^(n-1)+....oo=

If S_(n) denotes the sum of first 'n' natural numbers then S_(1)+S_(2)x+S_(3)x^(2)+........+S_(n)*x then n is

If S_(n) denotes the sum of first 'n' natural numbers then s_(1)+S_(2)x+S_(3)x^(2)+.........+S_(n) x^(n-1)+......oo=(1-x)^(-n) then n is

If s_(n) denotes the sum of first 'n' natural numbers then S_(1)+S_(2)x+S_(3)x^(2)+.........+S_(n)x^(n-1)+......oo=(1-x)^(-n) then n is

If S_(n) denotes the sum of first n terms of an AP, then prove that S_(12)=3(S_(8)-S_(4)).

S_(r) denotes the sum of the first r terms of an AP.Then S_(3d):(S_(2n)-S_(n)) is -

If S_(k) denotes the sum of first k terms of a G.P. Then, S_(n),S_(2n)-S_(n),S_(3n)-S_(2n) are in

If S_(n) denotes the sum of first n terms of an A.P., then (S_(3n)-S_(n-1))/(S_(2n)-S_(n-1)) is equal to