a: \(=-2\sqrt{5}+3\cdot3\sqrt{5}-6\cdot4\sqrt{5}-\dfrac{1}{5}\cdot5\sqrt{5}\)
\(=-2\sqrt{5}+9\sqrt{5}-24\sqrt{5}-\sqrt{5}=-18\sqrt{5}\)
d: \(=\dfrac{1}{\sqrt{2}}\left(\sqrt{10+2\sqrt{21}}+\sqrt{10-2\sqrt{21}}\right)-\sqrt{2}\cdot\sqrt{8-2\sqrt{7}}\)
\(=\dfrac{1}{\sqrt{2}}\cdot\left(\sqrt{7}+\sqrt{3}+\sqrt{7}-\sqrt{3}\right)-\sqrt{2}\left(\sqrt{7}-1\right)\)
\(=\dfrac{1}{\sqrt{2}}\cdot2\sqrt{7}-\sqrt{14}+\sqrt{2}\)
\(=\sqrt{2}\)
e: \(=\sqrt{\sqrt{5}-\sqrt{3-2\sqrt{5}+3}}\)
\(=\sqrt{\sqrt{5}-\sqrt{6-2\sqrt{5}}}\)
\(=\sqrt{\sqrt{5}-\sqrt{5}+1}=\sqrt{1}=1\)
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