SOLUTION: prove that: 1+2+3+....+n = n(n+1)/2

SOLUTION: prove that: 1+2+3+....+n = n(n+1)/2

Algebra.Com

Question 1126556: prove that: 1+2+3+....+n = n(n+1)/2
Answer by ikleyn(52776)   (Show Source): You can put this solution on YOUR website!
.
For the proof see the lessons
    - Arithmetic progressions
    - The proofs of the formulas for arithmetic progressions
    - Problems on arithmetic progressions
    - Mathematical induction and arithmetic progressions
in this site.

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