3 ms·

This proof helps: http://pirate.shu.edu/~wachsmut/ira/infinity/answers/sm_sq_cb.html http://pirate.shu.edu/~wachsmut/ira/infinity/answers/sm_sq_c... From that:

by hhm 19y ago

This proof helps: http://pirate.shu.edu/~wachsmut/ira/infinity/answers/sm_sq_cb.html http://pirate.shu.edu/~wachsmut/ira/infinity/answers/sm_sq_c... From that: sum bla= n(n+1)(2n+1)/6, then you go distribute

eru 19y ago
Nice. How did I get the result in the first place? I know that this sum can be expressed as a cubic polynomial. So I just evaluated the sum at four data-points (n=0,1,2,3) and used those to determine the four coefficents by solving a linear equation system.
- jgrahamc 19y ago
  Turns out that drawing a picture really helps: http://news.ycombinator.com/item?id=101532 http://news.ycombinator.com/item?id=101532
  - eru 19y ago
    You can usually come up with a clever picture only after you understood the problem - not before.