[tex]a)\\\sqrt{27}+\sqrt{12}-\sqrt{75}=\\=\sqrt{9*3}+\sqrt{4*3}-\sqrt{25*3}=\\
=\sqrt{9}\sqrt{3}+\sqrt{4}\sqrt{3}-\sqrt{25}\sqrt{3}=\\=3\sqrt{3}+2\sqrt{3}-5\sqrt{3}=\\
=(3+2)\sqrt{3}-5\sqrt{3}=\\=5\sqrt{3}-5\sqrt{3}=\\=(5-5)\sqrt{3}=\\=0\sqrt{3}=0[/tex]