as you know, complex roots come with their sister, the conjugate
thus, you have 2i, -2i, -8i, 8i
[tex]\bf \begin{cases}
x=2i\implies &x-2i=0\\
x=-2i\implies &x+2i=0\\
x=-8i\implies &x+8i=0\\
x=8i\implies &x-8i=0
\end{cases}
\\\\\\
(x-2i)(x+2i)(x+8i)(x-8i)=0\implies [x^2-(2i)^2][x^2-(8i)^2]=0
\\\\\\
(x^2+4)(x^2+64)=0\implies x^4+68x^2+256=0[/tex]
now, if we do f(-1), we'd end up with 323, not 325
so.. .what common factor can we stick there to get a 325?
well, let's say hmm "a" [tex]\bf a(323)=325\implies a=\cfrac{325}{323}[/tex]
there's our common factor
thus [tex]\bf \cfrac{325}{323}(x^4+68x^2+256)=0\implies \cfrac{325(x^4+68x^2+256)}{323}=0[/tex]
