[tex]1-4x^{2}-x(x^{2}-4)
=1-4x^{2}-x^{3}+4x
=4x(x+1)-(x^{3}+1)
=4x(x+1)-(x+1)(x^{2}-x+1)
= (x+1)(4x-x^{2}+x-1)
=-(x^{2}-5x-1)(x+1)
=-(x^{2}-2.x.\frac{5}{2}+\frac{25}{4}-1-\frac{25}{4})(x+1)
=-\left [(x-\frac{5}{2})^{2}-\frac{29}{4} \right ](x+1)
=-(x-\frac{5}{2}-\frac{\sqrt{29}}{2})(x-\frac{5}{2}+\frac{\sqrt{29}}{2})(x+1)[/tex]