\(x^4+x^3-8x-8=\left(x^4+x^3\right)+\left(-8x-8\right)\)
\(=x^3\left(x+1\right)-8\left(x+1\right)=\left(x+1\right)\left(x^3-8\right)\)
\(=\left(x+1\right)\left(x-2\right)\left(x^2+2x+2^2\right)=\left(x+1\right)\left(x-2\right)\left(x^2+2x+4\right).\)
\(=x^3\left(x-1\right)-8\left(x-1\right)=\left(x^3-8\right)\left(x-1\right)=\left(x-2\right)\left(x^2+2x+4\right)\left(x-1\right)\)