\(x^2+16x-225=0\)
\(\Leftrightarrow x^2+2.x.8+8^2-289=0\)
\(\Leftrightarrow\left(x+8\right)^2=289\)
\(\Leftrightarrow\left[{}\begin{matrix}x+8=17\\x+8=-17\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=9\\x=-25\end{matrix}\right.\)
Vậy \(\left[{}\begin{matrix}x=9\\x=-25\end{matrix}\right.\)
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