cach cua cac ban deu cho ra mot ket qua dung thanks

Ta có:(n²+n-1)\(⋮\left(n-1\right)\)

^{\(\Rightarrow n^2⋮\left(n-1\right)\)}

\(\Rightarrow n.\left(n-1\right)+1⋮\left(n-1\right)\)

\(\Rightarrow\left(n+1\right)⋮n-1\)

\(\Rightarrow n-1+2⋮n-1\)\

\(\Rightarrow2⋮n-1\)

\(\Rightarrow n-1\inƯ\left(2\right)\)

\(Ư\left(2\right)=1;2\)

Suy ra n=2