\[\left| x^{2} - 5x + 7 \right| - \left| - x^{2} + 4x - 6 \right| =\]
\[= \left| x^{2} - 5x + 7 \right| - \left| x^{2} - 4x + 6 \right| =\]
\[Дополнительные\ вычисления:\]
\[x^{2} - 5x + 7 =\]
\[= \left( x^{2} - 5x + 6\frac{1}{4} \right) + \frac{3}{4} =\]
\[= \left( x - \frac{5}{2} \right)^{2} + \frac{3}{4} > 0\]
\[x^{2} - 4x + 6 =\]
\[= \left( x^{2} - 4x + 4 \right) + 2 =\]
\[= (x - 2)^{2} + 2 > 0.\]