Finding Sum Using nth term

The first and the last terms of an A.P.are a and l respectively.Show that the sum of nth term from the beginning and nth term from the end is a+l

(i) The sum of the first n terms of an AP is ((5n^(2))/(2) + (3n)/(2)) . Find the nth term and the 20th term of this AP. (ii) The sum of the first n terms of an AP is ((3n^(2))/(2) + (5n)/(2)). Find its nth term and the 25th term.

Find the sum of n terms of the series whose nth terms is (i) n(n-1)(n+1) .

Find the sum of n terms of the series whose nth terms is (ii) n^(2)+3^(n) .

Find the sum to n terms of the series whose nth term is n^2+2^n .

The nth term of a G.P. is 3cdot(-2)^(n). Find the sum of its 7 terms.

Find the sum of 'n' terms of an A.P. whose nth term is 2n+1.

Find the sum of n terms of an A.P. whose nth term is (2n+1).

Find the sum to n terms of an A.P.whose nth terms is t_(n)=5+6n,n in N