If the sum of first `m` terms of an A.P. is the same as the sum of its first `n` terms, show that the sum of tis `(m+n)` terms is zero.

If the sum of m terms of an AP is the same as the sum of its n terms , show that the sum of its (m+n) terms is zero .

If the sum of first n terms of a G.P. is s and the sum of its first 2n terms is 5S, then show that the sum of its first 3n terms is 21S .

If the sum of first n terms of a G.P. is S and the sum of its first 2n terms is 5S, then show that the sum of its first 3n terms is 21S.

If the sum of m terms of an A.P. is same as the sum of its n terms, then the sum of its (m+n) terms is

If the sum of first p terms of an A.P. is equal to the sum of the first q terms, then find the sum of the first (p+q) terms.

If the sum of the first 9 terms of an AP is equal to the sum of its first 11 terms, then find the sum of its first 20 terms.

If the sum of the first 9 terms of an AP is equal to the sum of its first 11 terms, then find the sum of its first 20 terms.

If the sum of first n terms of an A.P. is 3n^(2)-2n , then its 19th term is