\(\frac{x^5+x+1}{x^3-1}=\frac{x^5-x^2+x^2+x+1}{x^3-1}=\frac{x^2\left(x^3-1\right)+\left(x^2+x+1\right)}{x^3-1}\)
\(=\frac{x^2\left(x-1\right)\left(x^2+x+1\right)+\left(x^2+x+1\right)}{\left(x-1\right)\left(x^2+x+1\right)}=\frac{\left(x^2+x+1\right)\left[x^2\left(x-1\right)+1\right]}{\left(x-1\right)\left(x^2+x+1\right)}\)
\(=\frac{x^3-x^2+1}{x-1}\)