$\dfrac{n^4-n^3+2n^2-n+1}{n^4+n^3+2n^2+n+1}$
$=\dfrac{n^4-n^3+n^2+n^2-n+1}{n^4+n^3+n^2+n^2+n+1}$
$=\dfrac{n^2(n^2-n+1)+(n^2-n+1)}{n^2(n^2+n+1)+(n^2+n+1)}$
$=\dfrac{(n^2+1)(n^2-n+1)}{(n^2+1)(n^2+n+1)}$
$=\dfrac{n^2-n+1}{n^2+n+1}$
Chúc bạn học tốt !!!!!