`(x-1)^2=9`
`=> (x-1)^2=3^2`
\(\Rightarrow\left[{}\begin{matrix}x-1=3\\x-1=-3\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=3+1\\x=-3+1\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=4\\x=-2\end{matrix}\right.\)
\(\left(x-1\right)^2=9< =>\left[{}\begin{matrix}x-1=3\\x-1=-3\end{matrix}\right.< =>\left[{}\begin{matrix}x=4\\x=-2\end{matrix}\right.\)