Il limite si presenta in forma indeterminata.
Risulta, razionalizzando il denominatore
[math]\displaystyle \lim_{{{n}\rightarrow\infty}}{n}-{\frac{{\sqrt{{{n}}}}}{{\sqrt{{{n}+{2}}}-\sqrt{{{n}+{1}}}}}}=[/math]
[math]\displaystyle \lim_{{{n}\rightarrow\infty}}{n}-{\frac{{\sqrt{{{n}}}\cdot{\left\lbrace\sqrt{{{n}+{2}}}+\sqrt{{{n}+{1}}}\right\rbrace}}}{{{1}}}}=[/math]
[math] \lim_{n \rightarrow\infty} n-\Big[\sqrt{n}\cdot\sqrt{n}\cdot\big(\sqrt{1+\frac{2}{n}}+\sqrt{1+\frac{1}{n}}\Big)\Big] =[/math]
[math]\displaystyle \lim_{n\rightarrow\infty} n\cdot\Big[1-\Big(\sqrt{1+\frac{2}{n}}+\sqrt{1+\frac{1}{n}}\Big)\Big]= +\infty\cdot {-1}=-\infty[/math]