toán trong violympic vòng 10 nè

B

braga

Ta có:

[TEX]1+2+3+.......+n=\frac{n(n+1)}{2}=2145 \to n(n+1)=4290[/TEX]

Mặt khác [TEX]4290=65.66[/TEX]

Vậy [TEX]n=\fbox{65}[/TEX]
 
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