\[y = - 3x^{2} + 9\]
\[- 3x² + 9 = 0\]
\[- 3x^{2} = - 9\]
\[x^{2} = 3\]
\[x = \pm \sqrt{3}.\]
\[Нули\ функции\ при\ x = \pm \sqrt{3}.\]