Odpowiedź:
[tex]a)\ \ (\sqrt{5}+2)(\sqrt{5}-2)=(\sqrt{5})^2-2^2=5-4=1\\\\\\b)\ \ (\sqrt{5}-\sqrt{2})(\sqrt{2}+3\sqrt{5})=\sqrt{10}+3\sqrt{25}-\sqrt{4}-3\sqrt{10}=\sqrt{10}+3\cdot5-2-3\sqrt{10}=\\\\=-2\sqrt{10}+15-2=-2\sqrt{10}+13\\\\\\c)\ \ (5+\sqrt{2})(\sqrt{8}-1)-9\sqrt{2}(1+\sqrt{2})=5\sqrt{8}-5+\sqrt{16}-\sqrt{2}-9\sqrt{2}-9\sqrt{4}=\\\\=5\sqrt{4\cdot2}-5+4-\sqrt{2}-9\sqrt{2}-9\cdot2=5\cdot2\sqrt{2}-1-10\sqrt{2}-18=\\\\=10\sqrt{2}-19-10\sqrt{2}=-19[/tex]
