`(3x-1)^2=x^2`
`<=>(3x-1)^2-x^2=0`
`<=>(3x-1-x)(3x-1+x)=0`
`<=>(2x-1)(4x-1)=0`
`<=>`$\left[\begin{matrix} 2x-1=0 \\ 4x-1=0 \end{matrix}\right.$
`<=>`$\left[\begin{matrix} x=\dfrac{1}{2} \\ x=\dfrac{1}{4} \end{matrix}\right.$
Vậy `x\in{1/2;1/4}`
`x^2-8x+16=0`
`<=>x^2-2.4.x+4^2=0`
`<=>(x-4)^2=0`
`<=>x-4=0`
`<=>x=4`
Vậy `x=4`