a, \(x^5+x^4+1\)
\(\Leftrightarrow x^5+x^4-x^2+\frac{1}{4}-\frac{1}{4}+x^2\)
\(\Leftrightarrow x^5+\left(x^2-\frac{1}{2}\right)^2-\frac{1}{4}+x^2\)
\(\Leftrightarrow x^2\left(x^3+1\right)+\left(x^2-\frac{1}{2}\right)^2-\frac{1}{4}\)
\(\Leftrightarrow x^2\left(x+1\right)\left(x^2-x+1\right)+\left(x^2-\frac{1}{2}+\frac{1}{2}\right)\left(x^2-\frac{1}{2}-\frac{1}{2}\right)\)
ta có :x^5 +x^4 +1=x^5-x^2 +x^4 -x +x^2 +x +1=x^2(x^3-1) +x(x^3 -1)+x^2 +x +1=x^2(x-1)(x^2+x+1)+x(x-1)(x^2 +x+1) +x^2 +x +1=(x^2 +x +1)(x^3 -x^2 +x^2 -x +1)=(x^2 +x+1)(x^3-x+1)
ta có x^5 +x +1=x^5-x^2 +x^2+x+1=x^2(x^3-1) +x^2 +x+1=x^2(x-1)(x^2+x+1)+x^2+x+1=(x^2+x+1)(x^3-x^2+1)