Question

The sum of first n terms of an A. P is 3n+n²then find first term and sum of first two terms.

Answer 1

Sn = n/2[ 2a + (n-1)d] = 3n + n^2

Sum of 1 term = first term = 3(1) + (1)^2 = 4 !! put n = 1

Sum of first 2 terms = 3(2)+(2)^2 = 6 + 4 = 10 !! put n = 2