\[\boxed{\text{639\ (639).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ x_{1} = \frac{\sqrt{3} - 1}{2};\ \ \ \ x_{2} = \frac{\sqrt{3} + 1}{2}\]
\[\left( x - x_{1} \right)\left( x - x_{2} \right) = 0\]
\[\left( x - \frac{\sqrt{3} - 1}{2} \right)\left( x - \frac{\sqrt{3} + 1}{2} \right) = 0\]
\[x^{2} - \frac{2\sqrt{3}}{2}x + \frac{2}{4} = 0\]
\[x^{2} - \sqrt{3}x + \frac{1}{2} = 0;\ \]
\[2x^{2} - \sqrt{3x} + 1 = 0 - искомое\ \]
\[уравнение.\ \]
\[\textbf{б)}\ x_{1} = 2 - \sqrt{3};\ \ x_{2} = \frac{1}{2 - \sqrt{3}}\]
\[\left( x - x_{1} \right)\left( x - x_{2} \right) = 0\]
\[\left( x - \left( 2 - \sqrt{3} \right) \right)\left( x - \frac{1}{2 - \sqrt{3}} \right) =\]
=\(0\)
\[x^{2} - \frac{8 - 4\sqrt{3}}{2 - \sqrt{3}}x + 1 = 0\]
\[x^{2} - \frac{4 \cdot \left( 2 - \sqrt{3} \right)}{2 - \sqrt{3}}x + 1 = 0\]
\[x^{2} - 4x + 1 = 0 - искомое\ \]
\[уравнение.\ \]