\[x^{2} + x - 20 = 0\]
\[x_{1} + x_{2} = - 1\]
\[x_{1} \cdot x_{2} = - 20\]
\[\Longrightarrow x_{1} = - 5;\ \ x_{2} = 4.\]
\[x² + x - 20 = (x + 5)(x - 4).\]