" (32) In an A.P.find "S_(n)" ,where "a_(n)=5n-1" .Hence find the sum of the first "20" terms."

The sum of the first n terms of an A.P.is 3n+n^(2) find "(1)" the first term "(2)" and the sum of the first two terms

Find the sum of first n terms of an AP whose nth term is (5n-1). Hence,find the sum of first 20 terms.

In an A.P., S_(m) = n and S_(n) = m also m gt n ,find the sum of first (m-n) terms .

If the sum of n terms of an A.P is cn (n-1) where c ne 0 then find the sum of the squares of these terms.

If the sum of n terms of an A.P is cn (n-1) where c ne 0 then find the sum of the squares of these terms.

If a_(1)=3 and a_(n)=n+a_(n-1) , the sum of the first five term is

Show that a_(1), a_(2), ….,a_(n),… form an A.P where an is defined as below : (i) a_(n) = 3 + 4n (ii) a_(n) = 9 - 5n . Also find the sum of the first 15 terms in each case.

Show that a_(1),a_(2),*a_(n),... form an AP where a_(n) is defined as below: (i) a_(n)=3+4n (ii) a_(n)=9-5n Also find the sum of the first 15 terms in each case.