\(=\dfrac{\sqrt{5}\left(\sqrt{5}+\sqrt{3}\right)\left(5-\sqrt{15}\right)}{\sqrt{5}}=\dfrac{\left(5+\sqrt{15}\right)\left(5-\sqrt{15}\right)}{\sqrt{5}}=\dfrac{25-15}{\sqrt{5}}=\dfrac{10}{\sqrt{5}}=2\sqrt{5}\)
\(\left(\sqrt{5}+\sqrt{3}\right)\left(5-\sqrt{15}\right)\\ =\left(\sqrt{5}+\sqrt{3}\right)\left(\sqrt{5}.\sqrt{5}.\sqrt{3}.\sqrt{3}\right)\\ =\left(\sqrt{5}+\sqrt{3}\right)\sqrt{5}\left(\sqrt{5}-\sqrt{3}\right)\\ =\sqrt{5}\left(5-3\right)\\ =2\sqrt{5}\)
\(\left(\sqrt{5}+\sqrt{3}\right)\left(5-\sqrt{15}\right)=\dfrac{\sqrt{5}\left(\sqrt{5}+\sqrt{3}\right)\left(5-\sqrt{15}\right)}{\sqrt{5}}\)
\(=\dfrac{\left(5+\sqrt{15}\right)\left(5-\sqrt{15}\right)}{\sqrt{5}}=\dfrac{5^2-\left(\sqrt{15}\right)^2}{\sqrt{5}}\)
\(=\dfrac{25-15}{\sqrt{5}}=\dfrac{10}{\sqrt{5}}=2\sqrt{5}\)
