\[x^{2} + 14x + 48 = (x + 8)(x + 6)\]
\[x^{2} + 14x + 48 =\]
\[= x^{2} + 6x + 8x + 48\]
\[= x^{2} + 14x + 48 \Longrightarrow ч.т.д.\]