Deduce a closed formula for the sum of arithmetic progression $$1+2+3+\ldots+n$$ using the fundamental theorem of the difference calculus.

| | | | created: 2020-05-17 10:58:32 | modified: 2020-05-17 11:14:03 | by: *bookofproofs* | references: [8404]

[8404] **Miller, Kenneth S.**: “An Introduction to the Calculus of Finite Differences And Difference Equations”, Dover Publications, Inc, 1960