2020-12-25

## sequences and series – Proof $1+2+3+4+\cdots+n = \frac{n\times(n+1)}2$

The Question : 115 people think this question is useful Apparently $1+2+3+4+\ldots+n = \dfrac{n\times(n+1)}2$. How? What’s the proof? Or maybe it is self apparent just looking at the above? PS: This problem is known as “The sum of the first $n$ positive integers”. The Question Comments : This an important example of a finite integral,