\[5x² - 20 = 0\ \ \ \ \ \ \ \ \ |\ :5\]
\[x^{2} - 4 = 0\]
\[(x - 2)(x + 2) = 0\]
\[x - 2 = 0,\ \ x + 2 = 0\]
\[x = 2\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = - 2\]
\[Ответ:\ x = - 2;x = 2.\]