a: \(=\left(x+2\right)\left(x^2-2x+4\right)-4x\left(x+2\right)\)
\(=\left(x+2\right)\left(x^2-6x+4\right)\)
b: \(=x^3-x^2-4x^2+4x+4x-4\)
\(=\left(x-1\right)\left(x^2-4x+4\right)=\left(x-1\right)\left(x-2\right)^2\)
c: \(=x^3+x^2+2x^2+2x+4x+4=\left(x+1\right)\left(x^2+2x+4\right)\)