\[x^{2} + px - 8 = 0;\ \ \ \ \ x_{1} = - 2\]
\[( - 2)^{2} + ( - 2)p - 8 = 0\]
\[4 - 2p - 8 = 0\]
\[- 2p = 4\]
\[p = - 2.\]
\[x^{2} - 2x - 8 = 0\]
\[x_{1} + x_{2} = 2\]
\[- 2 + x_{2} = 2\]
\[x_{2} = 4.\]
\[Ответ:x_{2} = 4;\ \ \ p = - 2.\]