👤

rezolvati [tex] 1^{2} +2^{2} +3^{2} +4^{2}+...n^{2}\ \textless \ \frac{ (2n+1)^{2} }{6} [/tex]

Răspuns :


[tex] \frac{n(n+1)(2n+1)}{6} [/tex] < [tex] \frac{ (2n+1)^{2} }{6} [/tex]

n(n+1)(2n+1) < [tex](2n+1)^{2} [/tex]

[tex]-2 n^{3}+ n^{2} + 3n + 1 \ \textgreater \ 0 [/tex]

Care este adevarat pentru oricare n<0

Solutia: n ∈ (-∞ , 0)