Dati $ a_1,a_2,...,a_n $ reali a somma nulla, qual è il valore di:
$ \displaystyle \sum_{j = 1}^n{\frac {1}{a_j(a_j + a_{j + 1})(a_j + a_{j + 1} + a_{j + 2})...(a_j + a_{j + 1} + ... + a_{j + n - 2})} \text { dove} a_{n + k} = a_k $ ?
Oliforum contest- round3- fake edition#2
Oliforum contest- round3- fake edition#2
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