Đáp án:
$\begin{array}{l}
\dfrac{{\sqrt 7 - 5}}{2} - \dfrac{{6 - 2\sqrt 7 }}{4} + \dfrac{6}{2} + \dfrac{{\sqrt 7 - 5}}{{\sqrt 7 }} - 2\\
= \dfrac{{\sqrt 7 }}{2} - \dfrac{5}{2} - \dfrac{6}{4} + \dfrac{{\sqrt 7 }}{2} + 3 + 1 - \dfrac{{5\sqrt 7 }}{7} - 2\\
= \left( {\dfrac{1}{2} + \dfrac{1}{2} - \dfrac{5}{7}} \right).\sqrt 7 + 2 - 4\\
= \dfrac{{2\sqrt 7 }}{7} - 2
\end{array}$