Một cách khác dài hơn -.-
\(\left(2x-5\right)^2-\left(x+2\right)^2=0\)
\(\Leftrightarrow4x^2-20x+25-x^2-4x-4=0\)
\(\Leftrightarrow3x^2-24x+21=0\)
\(\Leftrightarrow\left(3x^2-21x\right)-\left(3x-21\right)=0\)
\(\Leftrightarrow x\left(3x-21\right)-\left(3x-21\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(3x-21\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\3x-21=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=7\end{matrix}\right.\)
Vậy--...
