`a)(x^2+1)(x-2)+2x-4=0`
`=>(x^2+1)(x-2)+2(x-2)=0`
`=>(x-2)(x^2+3)=0`
`=>x=2`
Vậy `x=2`
`b)x^4-16x^2=0`
`=>x^4-8x^2-8x^2+64=0`
`=>x^2(x^2-8)-8(x^2-8)=0`
`=>(x^2-8)^2=0`
`=>`$\left[\begin{matrix}x^2-8=8\\ x^2-8=-8\end{matrix}\right.$
`=>`$\left[\begin{matrix} x^2=16\\ x^2=0\end{matrix}\right.$
`=>`$\left[\begin{matrix} x=+-4\\ x=0\end{matrix}\right.$
Vậy `x={4; -4; 0}`