Объяснение:

[tex]1)\ \frac{3}{\sqrt{5} }=\frac{3*\sqrt{5} }{\sqrt{5}*\sqrt{5} }=\frac{3\sqrt{5} }{5} .\\ 2)\ \frac{1}{3+\sqrt{2} }=\frac{3-\sqrt{2} }{(3+\sqrt{2} )*(3-\sqrt{2}) }= \frac{3-\sqrt{2} }{9-2} =\frac{3-\sqrt{2} }{7} .\\ 3)\ \frac{\sqrt{5}-\sqrt{7} }{\sqrt{5}+\sqrt{7} } =\frac{(\sqrt{5}-\sqrt{7})*(\sqrt{5}-\sqrt{7}) }{(\sqrt{5}+\sqrt{7})*( \sqrt{5}-\sqrt{7}) } =\frac{(\sqrt{5}-\sqrt{7})^2 }{5-7}=\frac{5-2\sqrt{5*7} +7}{-2} =\frac{12-2\sqrt{35} }{-2}= \sqrt{35}-6.[/tex]