Question

Aflati numarul natural nenul x stiind ca:
(1+2+3+...+×)÷×=55

Answer 1

 [tex]\underbrace{(1+2+3+...+x)}_{=\frac{x\cdot(x+1)}{2}}:x=55\\ \Rightarrow\;\frac{x+1}{2}=55\;\rightarrow\;x+1=55*2\;deci\,\fbox{x=109}\in\mathbb{N}[/tex]