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Bài 3)

a) $\displaystyle ( 2x-3)^{2} =( x+7)^{2}$

$\displaystyle  \begin{array}{{>{\displaystyle}l}}
\Leftrightarrow ( 2x-3)^{2} -( x+7)^{2} =0\\
\Leftrightarrow ( 2x-3-x-7)( 2x-3+x+7) =0\\
\Leftrightarrow ( x-10)( 3x+4) =0\\
\Leftrightarrow \left[ \begin{array}{l l}
x=10 & \\
x=\frac{-4}{3} & 
\end{array} \right.
\end{array}$

b) $\displaystyle x^{2} -9=3( x+3)$

$\displaystyle  \begin{array}{{>{\displaystyle}l}}
\Leftrightarrow ( x-3)( x+3) -3( x+3) =0\\
\Leftrightarrow ( x+3)( x-3-3) =0\\
\Leftrightarrow ( x+3)( x-6) =0\\
\Leftrightarrow \left[ \begin{array}{l l}
x=-3 & \\
x=6 & 
\end{array} \right.
\end{array}$

c) $\displaystyle x^{2} -x=-2x+2$

$\displaystyle  \begin{array}{{>{\displaystyle}l}}
\Leftrightarrow x^{2} -x+2x-2=0\\
\Leftrightarrow x( x-1) +2( x-1) =0\\
\Leftrightarrow ( x-1)( x+2) =0\\
\Leftrightarrow \left[ \begin{array}{l l}
x=1 & \\
x=-2 & 
\end{array} \right.
\end{array}$

d) $\displaystyle x^{2} -3x=2x-6$

$\displaystyle  \begin{array}{{>{\displaystyle}l}}
\Leftrightarrow x^{2} -3x-2x+6=0\\
\Leftrightarrow x( x-3) -2( x-3) =0\\
\Leftrightarrow ( x-3)( x-2) =0\\
\Leftrightarrow \left[ \begin{array}{l l}
x=3 & \\
x=2 & 
\end{array} \right.
\end{array}$