Question 873556: Arithmetic series: 1,3,6,10,15... What is the 8th term?
Answer by richwmiller(17219)   (Show Source):
You can put this solution on YOUR website!
The difference is not constant.
Differences are
2,3,4,5 the next difference is 6 so the next terms are 21,28,36,
36 is the 8th term
the second difference is 1
add n+1 to the last term
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