Câu 1 :đkxđ : x >0
[tex]x\sqrt{18900x}:\sqrt{210x}:\sqrt{10x}=\frac{x\sqrt{18900x}}{\sqrt{210x}.\sqrt{10x}}\\=\frac{x\sqrt{18900x}}{x\sqrt{2100}}=3\sqrt{x}[/tex]
Câu 2:
[tex]\frac{3+\sqrt{3}}{\sqrt{2}+2\sqrt{3}}[/tex]
[tex]=\frac{(3+\sqrt{3})(2\sqrt{3}-\sqrt{2})}{10}=\frac{6\sqrt{3}+6-\sqrt{6}-2\sqrt{2}}{10}[/tex]