Theory OF Sum OF First n Terms OF A.P

The sum of first n terms of an A.P.is 5n-n^(2) . Find the nth term of this A.P.

The sum of first n terms of an A.P. is 3n^2+4n . Find the 25 t h term of this A.P.

The sum of first n terms of an A.P. is 5n^(2) + 3n . If the nth term is 168, find the value of n. Also find the 20th term of the A.P.

The sum of first n terms of an A.P is given by 3n^(2)+6n The 22 nd term of the A.p.is

The sum of first n terms of an A.P. is 5n ^(2)+ 4n, its common difference is :

If the sum of first 7 terms of an A.P is 49 and that of its first 17 terms is 289, find the sum of first n terms of the A.P

If the sum of the first four terms of an AP is 40 and the sum of the first fourteen terms of an AP is 280. Find the sum of first n terms of the A.P.

If the sum of first 7 terms of an A.P. is 49 and that of its 17 terms is 289, find the sum of first n terms of the A.P.