\[5 - x^{2} = 1 - x(x + 8)\]
\[5 - x^{2} = 1 - x^{2} - 8x\]
\[- 8x = 5 - 1\]
\[- 8x = 4\]
\[x = - \frac{4}{8} = - \frac{1}{2}\]
\[x = - 0,5.\]