\[\boxed{\text{778.}\text{\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[x^{2} + px + 405 = 0\] | \[\left( x_{2} - x_{1} \right)^{2} = 144\] |
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\[\left\{ \begin{matrix} x_{1} + x_{2} = - p \\ x_{1}x_{2} = 405\ \ \ \ \\ \end{matrix} \right.\ \text{\ \ \ }\] |
\[\left( x_{2} - x_{1} \right)^{2} = x_{2}^{2} - 2x_{1}x_{2} + x_{1}^{2} =\] \[= x_{1}^{2} + x_{2}^{2} - 2x_{1}x_{2} = x_{1}^{2} + x_{2}^{2} -\] \[- 2 \cdot 405 = 144\ \ \] |
\[x_{1}^{2} + x_{2}^{2} - 810 = 144\]
\[x_{1}^{2} + x_{2}^{2} = 954\]
\[x_{1}^{2} + x_{2}^{2} = x_{1}^{2} + 2x_{1}x_{2} + x_{2}^{2} -\]
\[- 2x_{1}x_{2} = \left( x_{1} + x_{2} \right)^{2} - 2x_{1}x_{2} =\]
\[= ( - p)^{2} - 2 \cdot 405 = 954\]
\[p^{2} - 810 = 954\]
\[p^{2} = 1764\]
\[p = \pm 42\]
\[Ответ:p = \pm 42\text{.\ \ }\]