Letter D is:
[tex]f(x)=27x^3-18x^2-3x[/tex]'3x' is a common factor between all coefficients, thus:
[tex]f(x)\text{ = 3x}(9x^2-6x-1)[/tex]We can continue and factor 9x^2 - 6x - 1 but we have to find the roots (applying the Bhaskara equation to find the roots):
[tex]x\text{ = }\frac{6\pm\sqrt[]{36-4\times9\times(-1)}}{2\times9}[/tex]
