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