if nth term of an AP is (2n+1) find the sum of first n terms of AP

a_n = a + (n-1)d = (2n+1) ...........(1)

S_n = n(2a +(n-1)d)/2

= n(a + (2n+1))/2

where a is the first term, which can be obtained by (1) by using n = 1.

a = 3

S_n = n(3 + (2n+1))/2 = n(n+2)

Regards,

Team,

TopperLearning.