\(x^2-4x=32\)
\(\Leftrightarrow x^2-4x-32=0\)
\(\Leftrightarrow x^2-8x+4x-32=0\)
\(\Leftrightarrow x\left(x-8\right)+4\left(x-8\right)=0\)
\(\Leftrightarrow\left(x-8\right)\left(x+4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-8=0\\x+4=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=8\\x=-4\end{matrix}\right.\)
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