Question

the sum of first n terms of an arithmetic progression is given by sn= 3n²+n then it's 3rd term is
what is answer
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Answer 1

Answer:

Let S

n

be the sum of n terms of an AP with first term a and common difference d.

Since S

n

=3n

2

−n and d=6

⇒S

n

=

2

n

(2a+(n−1)d)=3n

2

−n

2

n

(2a+(n−1)6)=3n

2

−n

n(a+(n−1)3)=3n

2

−n

(a+3n−3)=3n−1

a=2