The sum of the first n terms of an arithmetic sequence is n^(2)+6n, Find the nth term of the sequence.

@Callisto

Question

The sum of the first n terms of an arithmetic sequence is n^(2)+6n, Find the nth term of the sequence.

@Callisto

callisto · Answer

Find the sum of n terms, and the sum of (n-1) terms using the formula. Then, find the nth term by subtracting the sum of (n-1) terms from the sum of n terms.

anonymous · Answer

(a+l)n / 2 ?

callisto · Answer

Just use the formula given in the question.

anonymous · Answer

oh

callisto · Answer

Got the idea?

anonymous · Answer

[(n-1)^(2) + 6(n-1) ] - n^(2)+6n ??

callisto · Answer

What one has a greater value - sum of n terms or sum of (n-1) terms?

anonymous · Answer

n^(2)+6n - [(n-1)^(2) + 6(n-1) ]

callisto · Answer

Yes, always (sum of n terms)  - (sum of (n-1) terms) to find the nth term.

If you do  (sum of (n-1) terms) - (sum of n terms), then you need to multiply the answer by -1 to get the nth term.

anonymous · Answer

ok, i understand now