Explicatie:
Il ridicam lapatrat pe 2√5
apoi il incadram intre 2 patrate perfecte consecutive.
Rezolvare:
[tex]\displaystyle\bf\\n-1<2\sqrt{5}<n\\\\\Big(2\sqrt{5}\Big)^2=4\times5=20\\\\16<20<25\\\\\implies~4<2\sqrt{5}<5\\\\5-1<2\sqrt{5}<5\\\\\implies~~\boxed{\bf n=5}[/tex]
Raspuns corect c)
