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Odd Sum (Posted on 2002-08-08) Difficulty: 2 of 5
Prove that the sum of consecutive odd numbers beginning at 1 (eg 1, 3, 5, ..) always adds up to a perfect square

See The Solution Submitted by Cheradenine    
Rating: 3.9000 (10 votes)

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Simplify a bit | Comment 6 of 17 |
The sum of 1+3+5+... is represented by ∑2n-1 where n runs from 1 to n. So the question is does this sum equal n², or

∑2n-1 = n² ?

Taking the 2 and the 1 out of the summation gives:

2(∑n)-n = n²

Moving the 2 and the -n to the other side gives:

∑n = (n²-n)/2 = n(n+1)/2

Look familiar?
  Posted by Jack Squat on 2004-01-05 14:17:06
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