Question 720845
General arithmetic sequence term is {{{a[1]+d(n-1)}}}, where n is a natural number, the index of a term.  Based on that, what can you say about the term at n=5?  Can you find a formula for the first n terms of an arithmetic sequence?  Maybe refer to your book, or derive it yourself?


You should find that the sum of the first n terms of an arithmetic sequence is {{{(n/2)(a[1]+a[n])}}}.