[tex]x^4 +2x^3 -11x^2-12x+36\\ \\=x^4-2x^3+4x^3-8x^2-3x^2 +6x-18x+36\\\\=x^3(x-2) +4x^2(x-2) -3x(x-2) -18(x-2)\\\\=(x-2)(x^3 +4x^2 -3x -18)\\\\=(x-2)(x^3+3x^2+x^2+3x-6x-18)\\\\=(x-2)\textbf{[}x^2(x+3)+x(x+3)-6(x+3)\textbf{]}\\\\=(x-2)(x+3)(x^2 +x -6)\\\\=(x-2)(x+3)(x^2 +3x -2x-6)\\\\=(x-2)(x+3)\textbf{[}x(x+3) -2(x+3)\textbf{]}\\\\=(x-2)(x-2)(x+3)(x+3)\\\\=(x-2)^2(x+3)^2[/tex]
