Question

What's the sum Sn of the first n terms of this given sequence?

1, 1+2, 1+2+3, 1+2+3+4, ...
The kth term is 1+2+3+ ... +k =

(I also attached a picture of the question. Thanks!)
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Answer 1

Answer:
`(k(k+1))/(2)`

Explanation:

This is a standard formula.