Đề bài vô lí nhé !
\(x^2-9x+2=0\)
\(\Leftrightarrow x^2-2.x.\frac{9}{2}+\frac{81}{4}-\frac{73}{4}=0\)
\(\Leftrightarrow\left(x-\frac{9}{2}\right)^2=\frac{73}{4}\)
\(\Leftrightarrow\left[{}\begin{matrix}x-\frac{9}{2}=\frac{\sqrt{73}}{2}\\x-\frac{9}{2}=\frac{-\sqrt{73}}{2}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\frac{\sqrt{73}+9}{2}\\x=\frac{-\sqrt{73}+9}{2}\end{matrix}\right.\)
Vậy \(x\in\left\{\frac{\sqrt{73}+9}{2};\frac{-\sqrt{73}+9}{2}\right\}\)
