If the nth term of an A.P. is(3n + 1). then the
sum of its first ‘n terms is
A
2n2 +4n
3
3n2 +4n
B

September 10, 2021

By Autumn

1 thought on “If the nth term of an A.P. is(3n + 1). then the<br />sum of its first ‘n terms is<br />A<br />2n2 +4n<br />3<br />3n2 +4n<br />B<b”

1. Step-by-step explanation:

   Tn=Sn−Sn−1 .(1)

   Now Sn=3n2+4n

   ∴Sn−1=3(n−1)2+4(n−1)=3n2−2n−1

   ∴Tn=(3n2−4n)−(3n2−2n−1), by (1)

   =6n+1

   ∴T1=7,T2=13,T3=19,______

   ∴a=7,d=6.

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