sum of first n integers.
回答 (1)
2014-02-23 2:44 am
✔ 最佳答案
Let S=1+2+...+nAlso, S=n+(n-1)+...+1
Adding gives, 2S=(n+1)+(n+1)+(n+1)+...+(n+1)
thus, 2S=n(n+1) which gives S=n(n+1)/2
Proved.
I have 8 more proofs from different approach, you may email me via http://ck-math.com
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