=(x2 -4x2)-((x2-2x)(x+2))
=(x2-4x2)-(x3+2x2-2x2-4x)
=x2-4x2-x3+4x
=-x3-3x2+4x=-x(x2+3x-4)
\(\left(x-2x\right)\left(x+2x\right)-x\left(x-2\right)\left(x+2\right)\)
\(=x^2-4x^2-x\left(x^2-4\right)\)
\(=x^2-4x^2-x^3+4x\)
\(=x^2-x^3-4x^2+4x\)
\(=x^2\left(x-1\right)-4x\left(x-1\right)\)
\(=\left(x-1\right)\left(x^2-4x\right)\)
\(=x\left(x-1\right)\left(x-4\right)\)