\[x² + 8x - 13 = 0\]
\[D = 8^{2} - 4 \cdot 1 \cdot ( - 13) =\]
\[= 64 + 52 = 116\]
\[x_{1} = \frac{- 8 + \sqrt{116}}{2 \cdot 1} = \frac{- 8 + 2\sqrt{29}}{2} =\]
\[= - 4 + \sqrt{29}\]
\[x_{2} = \frac{- 8 - \sqrt{116}}{2 \cdot 1} = \frac{- 8 - 2\sqrt{29}}{2} =\]
\[= - 4 - \sqrt{29}\]
\[Ответ:\ x = - 4 + \sqrt{29};\ \]
\[x = - 4 - \sqrt{29}.\]