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Question Number 21282 by youssoufab last updated on 18/Sep/17

s o i t {(u_{n})}_{n \in N^{*}} u n e s u i t e a t e r m e s p o s i t i f s t e l l e q u e :

\forall n \in N^{*}, \underset{k = 1}{\sum^{n}} u_{k}^{3} = {(\underset{k = 1}{\sum^{n}} u_{k})}^{2}

m o n t r e r q u e \forall n \in N^{*}, u_{n} = n