Question 306836
Complex roots always occur in complex conjugate pairs.
Since (1+2i) is a solution, (1-2i) is also a solution. 
{{{f(x)=A(x-4)(x-3)(x+1/3)(x-(1+2i))(x-(1-2i))}}}
{{{f(1)=A(1-4)(1-3)(1+1/3)(1-1-2i)(1-1+2i)=64}}}
{{{A(-3)(4/3)(-2i)(2i)=64}}}
{{{A(-4)(-4i^2)=64}}}
{{{A(-16)=64}}}
{{{A=-4}}}
{{{f(x)=-4(x-4)(x-3)(x+1/3)(x-(1+2i))(x-(1-2i))}}}