If the sum of first n terms of an A.P. be 3n2+n . . .

Question : If the sum of first n terms of an A.P. be 3n²+n and its common difference is 6, then its first term is

a) 2

b) 3

c) 1

d) 4

Doubt by Vikrant

Solution : 
Sn=3n²+n
d = 6

We know, 
S₁=a₁=3(1)²+(1)
S₁=a₁=3(1)+1
S₁=a₁=3+1
S₁=a₁=4

The first term of the AP is 4. 
Hence, d) 4, would be the correct option.