a5+a+1=a5+a4+a3+a2+a+1-a4-a3-a2
=a3.(a2+a+1)+(a2+a+1)-a2.(a2+a+1)
=(a2+a+1)(a3-a2+1)
Ta có : \(a^5+a+1=\left(a^5-a^2\right)+\left(a^2+a+1\right)\)
\(=a^2\left(a^3-1\right)+\left(a^2+a+1\right)\)
\(=a^2\left(a-1\right)\left(a^2+a+1\right)+\left(a^2+a+1\right)\)
\(=\left(a^2+a+1\right)\left(a^3-a^2+1\right)\)
\(a^5+a+1=a^5+a^4+a^3+a^2+a+1-a^4-a^3-a^2\)
\(=a^2\left(a^3-1\right)+\left(a^2+a+1\right)\)
\(=a^2\left(a-1\right)\left(a^2+a+1\right)+\left(a^2+a+1\right)\)
\(=\left(a^2+a+1\right)\left(a^3-a^2+1\right)\)
Chúc bạn học tốt 
