\(\Leftrightarrow x^4-18x^2+81-4x^2-8x-4=0\)
\(\Leftrightarrow\left(x^2-9\right)^2-\left(2x+2\right)^2=0\)
\(\Leftrightarrow\left(x^2-9-2x-2\right)\left(x^2-9+2x+2\right)=0\)
\(\Leftrightarrow\left(x^2-2x-10\right)\left(x^2+2x-7\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x^2-2x-10=0\\x^2+2x-7=0\end{cases}\Leftrightarrow\orbr{\begin{cases}\left(x-1\right)^2=\pm\left(\sqrt{11}\right)^2\\\left(x+1\right)^2=\pm\left(\sqrt{8}\right)^2\end{cases}}}\)
ĐẾN ĐÂY BẠN TỰ LÀM NHÉ
X= \(1+\sqrt{11}\),X=\(-1+\sqrt{11}\)
X=\(-1-2\sqrt{2}\),X=\(-1+2\sqrt{2}\)
\(\Leftrightarrow\orbr{\begin{cases}\left(x-1\right)^2=\pm\left(\sqrt{11}\right)\\\left(x+1\right)^2=\pm\left(\sqrt{8}\right)\end{cases}\Leftrightarrow\orbr{\begin{cases}\orbr{\begin{cases}x=1+\sqrt{11}\\x=1-\sqrt{11}\end{cases}}\\\orbr{\begin{cases}x=-1+2\sqrt{2}\\x=-1-2\sqrt{2}\end{cases}}\end{cases}}}\)
