\(a.\left(\sqrt{3}+\sqrt{5}\right)\sqrt{7-2\sqrt{10}}=\left(\sqrt{3}+\sqrt{5}\right)\sqrt{5-2\sqrt{5}.\sqrt{2}+2}=\left(\sqrt{3}+\sqrt{5}\right)\left(\sqrt{5}-\sqrt{2}\right)\) \(b.\left(2+\sqrt{5}\right)\sqrt{9-4\sqrt{5}}=\left(2+\sqrt{5}\right)\sqrt{5-2.2\sqrt{5}+4}=\left(2+\sqrt{5}\right)\left(\sqrt{5}-2\right)=5-4=1\)