\[x^{2} + px - 72 = 0;\ \ \ \ x_{1} = 9\]
\[q = x_{1} \cdot x_{2}\]
\[9x_{2} = - 72\]
\[x_{2} = - 8.\]
\[x_{1} + x_{2} = - p\]
\[9 - 8 = - p\]
\[- p = 1\]
\[p = - 1.\]
\[Ответ:x_{2} = - 8;\ \ p = - 1.\]