Tính gía trị các căn sau

$$\begin{gathered} a/ ( 5\sqrt{2} - 2\sqrt{5} ) \times ( 5\sqrt{2} + 2\sqrt{5} ) \\ b/ \sqrt{4 + \sqrt{10 + 2\sqrt{5}}} + \sqrt{4 - \sqrt{10 + 2\sqrt{5}}} \\ c/ ( \sqrt{3} - 1) \times (\sqrt{6} + 2) \times \sqrt{2+\sqrt{3}} \\ d/ \sqrt{10 + \sqrt{60}+ \sqrt{40} + \sqrt{24}} \end{gathered}$$