\(a,x^7+x^5+1\)
\(=\left(x^7+x^6+x^5\right)-\left(x^6-1\right)\)
\(=x^5\left(x^2+x+1\right)-\left(x^3-1\right)\left(x^3+1\right)\)
\(=x^5\left(x^2+x+1\right)-\left(x-1\right)\left(x^2+x+1\right)\left(x^3+1\right)\)
\(=\left(x^2+x+1\right)\left(x^5-\left(x-1\right)\left(x^3+1\right)\right)\)
\(b,x^5-x^4-1\)
\(=x^5-x^4+x^3-x^3-1\)
\(=x^3\left(x^2-x+1\right)+\left(x+1\right)\left(x^2-x+1\right)\)
\(=\left(x^2-x+1\right)\left(x^3+x+1\right)\)
