a.
\(=\dfrac{\sqrt{48-6\sqrt{15}}-\sqrt{72-18\sqrt{15}}}{\sqrt{2}}=\dfrac{\sqrt{\left(3\sqrt{5}-\sqrt{3}\right)^2}-\sqrt{\left(3\sqrt{5}-3\sqrt{3}\right)^2}}{\sqrt{2}}\)
\(=\dfrac{3\sqrt{5}-\sqrt{3}-3\sqrt{5}+3\sqrt{3}}{\sqrt{2}}=\dfrac{2\sqrt{3}}{\sqrt{2}}=\sqrt{6}\)
b.
\(=\sqrt{\left(2\sqrt{2}-\sqrt{7}\right)^2}+\sqrt{\left(\sqrt{5}-2\sqrt{2}\right)^2}\)
\(=\left|2\sqrt{2}-\sqrt{7}\right|+\left|\sqrt{5}-2\sqrt{2}\right|\)
\(=2\sqrt{2}-\sqrt{7}+2\sqrt{2}-\sqrt{5}\)
\(=4\sqrt{2}-\sqrt{7}-\sqrt{5}\)
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