\(2\left(x-3\right)^4-3^2=503\\ \Rightarrow2\left(x-3\right)^4=512\\ \Rightarrow\left(x-3\right)^4=256\\ \Rightarrow\left[{}\begin{matrix}x-3=4\\x-3=-4\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=7\\x=-1\end{matrix}\right.\)
`2(x-3)^4-3^2=503`
`=>2(x-3)^4-9=503`
`=>2(x-3)^4=503+9`
`=>2(x-3)^4=512`
`=>(x-3)^4=512:2`
`=>(x-3)^4=256`
`=>(x-3)^4=4^4` hoặc `(x-3)^4=(-4)^4`
`=>x-3=4` hoặc `x-3=-4`
`=>x=7` hoặc `x=-1`
Vậy `x in{-1;7}`