\(\left(x-9\right)^4=81\\ =>\left[{}\begin{matrix}\left(x-9\right)^4=3^4\\\left(x-9\right)^4=\left(-3\right)^4\end{matrix}\right.=>\left[{}\begin{matrix}x-9=3\\x-9=-3\end{matrix}\right.=>\left[{}\begin{matrix}x=12\\x=6\end{matrix}\right.\)
\(\left(x-9\right)^4=81\\ TH1:\left(x-9\right)^4=3^4\\ x-9=3\\ x=3+9\\ x=12\\ TH2:\left(x-9\right)^4=\left(-4\right)^4\\ x=-3+9\\ x=6\)
\(\left(x-9\right)^4=81\)
\(\left(x-9\right)^4=3^4\)
\(\Rightarrow x-9=\pm3\)
\(TH1:x-9=3\)
\(x=12\)
\(TH2:x-9=-3\)
\(x=6\)
