[tex]-9x^2=-18x+7\ \ \ |+9x^2\\\\9x^2-18x+7=0\\\\a=9;\ b=-18;\ c=7\\\\\Delta=b^2-4ac\to\Delta=(-18)^2-4\cdot9\cdot7=324-252=72\\\\\sqrt\Delta=\sqrt{72}=\sqrt{36\cdot2}=\sqrt{36}\cdot\sqrt2=6\sqrt2\\\\x_1=\dfrac{-b-\sqrt\Delta}{2a};\ x_2=\dfrac{-b+\sqrt\Delta}{2a}\\\\x_1=\dfrac{18-6\sqrt2}{2\cdot9}=\dfrac{9-3\sqrt2}{9}=\dfrac{3-\sqrt2}{3}\\\\x_2=\dfrac{3+\sqrt2}{3}[/tex]
