Montrer :
1
\(\displaystyle{\sum_{k=1}^{n}k=\frac{n(n+1)}{2} \quad \forall n \in \Nn^{*} \,.}\)
2
\(\displaystyle{\sum_{k=1}^{n}k^2=\frac{n(n+1)(2n+1)}{6} \quad \forall n \in \Nn^{*} \,.}\)
Montrer :
\(\displaystyle{\sum_{k=1}^{n}k=\frac{n(n+1)}{2} \quad \forall n \in \Nn^{*} \,.}\)
\(\displaystyle{\sum_{k=1}^{n}k^2=\frac{n(n+1)(2n+1)}{6} \quad \forall n \in \Nn^{*} \,.}\)