PT \(\Leftrightarrow x^2-8x+15=0\)
\(\Leftrightarrow x^2-3x-5x+15=0\)
\(\Leftrightarrow x\left(x-3\right)-5\left(x-3\right)=0\)
\(\Leftrightarrow\left(x-5\right)\left(x-3\right)=0\) \(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=5\end{matrix}\right.\)
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