Question

The sum of first n terms of an arithmetic sequence is 3n^+n
Find the first term and common difference of this sequence
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Answer 1

Step-by-step explanation:

Sn=3n²+n.

If n=1,

A=S1=3{1)²+1=3+2=4.

If n=2

S2=3(2)²+1

=> 3×4+1

=> 12+1=13.

A2=S2-S1

=> 13-4=9

A=4, A2=12

common difference, d=second term-first term.

=> 9-4

=> 5.