\(x^2-4x-4=25\)
\(\Leftrightarrow x^2-4x+4=33\)
\(\Leftrightarrow\left(x-2\right)^2=33\)
\(\Leftrightarrow\orbr{\begin{cases}x-2=\sqrt{33}\\x-2=-\sqrt{33}\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=\sqrt{33}+2\\x=2-\sqrt{33}\end{cases}}\)
\(x^2-4x-4=25\)
\(\Rightarrow x^2-4x-4-25=0\)
\(\Rightarrow x^2-4x-29=0\)
\(\Rightarrow x^2-4x+4-33=0\)
\(\Rightarrow\left(x^2-4x+4\right)-33=0\)
\(\Rightarrow\left(x-2\right)^2=33\)
\(\Rightarrow\left(x-2\right)^2=\left(\sqrt{33}\right)^2=\left(-\sqrt{33}\right)^2\)
\(\Rightarrow\orbr{\begin{cases}x-2=\sqrt{33}\\x-2=-\sqrt{33}\end{cases}\Rightarrow\orbr{\begin{cases}x=2+\sqrt{33}\\x=2-\sqrt{33}\end{cases}}}\)
Vậy \(x\in\left\{2+\sqrt{33};2-\sqrt{33}\right\}\)
