\[x^{2} - 4x + 3\]
\[D = ( - 4)^{2} - 4 \cdot 1 \cdot 3 =\]
\[= 16 - 12 = 4\]
\[x_{1} = \frac{4 + \sqrt{4}}{2} = \frac{4 + 2}{2} = \frac{6}{2} = 3\]
\[x_{2} = \frac{4 - \sqrt{4}}{2} = \frac{4 - 2}{2} = \frac{2}{2} = 1\]
\[x^{2} - 4x + 3 = (x - 3)(x - 1).\]