Question

if the sum of the first term n term of 3nsquare +n. what is it's first term, common difference and write algebraic form?

Answer 1

Sn = 3n^2 + n

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

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

=> 2a + (n-1)d = 6n + 2

=> 2a + (n-1)d = 8 - 6 + 6n

=> 2a +(n-1) d = 8 + 6(n-1)

On comparing both sides, we get

2a = 8

=> a = 4

And,

d = 6

First term = 4

Common difference = 6

Tn = 4 + (n-1)6 = 4 + 6n - 6 = 6n - 2