\[x^{2} - px + 48 = 0\]
\[D = p^{2} - 4 \cdot 48 = p^{2} - 192\]
\[Так\ как\ уравнение\ имеет\ \]
\[2\ корня,\ то\ D > 0.\]
\[x_{1,2} = \frac{p \pm \sqrt{p² - 192}}{2}\]
\[По\ условию\ \ \ x_{1} = 3x_{2}:\]
\[2p - 4\sqrt{p^{2} - 192} = 0\]
\[(p)^{2} = \left( 2\sqrt{p^{2} - 192} \right)^{2}\]
\[p^{2} = 4p^{2} - 768\]
\[3p^{2} = 768\]
\[p^{2} = 256\]
\[p = \pm 16\]
\[Так\ как\ p > 0,\ \ \ то\ \ p = 16.\]
\[Ответ:p = 16.\]