\(\left(\sqrt{10}-\sqrt{2}\right)\sqrt{3+\sqrt{5}}=\left(\sqrt{5}-1\right)\sqrt{2}\sqrt{3+\sqrt{5}}\)
\(=\left(\sqrt{5}-1\right)\sqrt{6+2\sqrt{5}}=\left(\sqrt{5}-1\right)\sqrt{5+2\sqrt{5}+1}\)
\(=\left(\sqrt{5}-1\right)\sqrt{\left(\sqrt{5}+1\right)^2}=\left(\sqrt{5}-1\right)\left(\sqrt{5}+1\right)\)
\(=5-1=4\)