\(x^2+14x+48=0\)
\(\Leftrightarrow x^2+6x+8x+48=0\)
\(\Leftrightarrow x\left(x+6\right)+8\left(x+6\right)=0\)
\(\Leftrightarrow\left(x+6\right)\left(x+8\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x+6=0\\x+8=0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x=-6\\x=-8\end{array}\right.\)