[tex]\\\sqrt{75}+\sqrt{48}-\sqrt{300}\\=\sqrt{25}.\sqrt{3}+\sqrt{16}.\sqrt{3}-sqrt{100}.\sqrt{3}\\=5\sqrt{3}+4\sqrt{3}-10\sqrt{3}\\=-\sqrt{3}\\\sqrt{98}-\sqrt{72}+0,5\sqrt{8}\\=\sqrt{12,25}.\sqrt{8}-\sqrt{9}.\sqrt{8}+0,5\sqrt{8}\\=3,5\sqrt{8}-3\sqrt{8}+0,5\sqrt{8}\\=\sqrt{8}\\\sqrt{9a}- \sqrt{16a}+\sqrt{49a}\\=3\sqrt{a}-4\sqrt{a}+7\sqrt{a}\\=6\sqrt{a}\\[/tex]