If the `r^(th)` term of a series is `1 + x + x^2 + .......+ x^(r-1)` , then the sum of the first n terms is

The n^(th) term of the series a + a r + a r 2 + − − − − is

The rth term of a series is (2r + 1)2^(r ) , find the sum of first n terms of the series.

If the nth term of a series be (2.3^(n-1) + 1) , find the sum of first r terms of the series.

If r^(th) term of a series is (2r+1)2^(-r) then sum of its infinite terms is

If n th term of a-series be (2.3^(n-1)+1) ,, find the sum of 1st r terms of the series.

In a series, the rth term is (2r + 1).2r. Find the sum of 1st n terms of this series.

Find n^(th) term of the series 1+(1+2)+(1+2+3)+.... Find the sum to n terms of the series

If the sum of first n terms which are in GP is a(r+1) , then the number of terms is _____. (Where a is the first term and r is the common ratio)

The sum of first r terms of a series is ar^(2) + br , find the first and 12th terms of the series.