Rút gọn biểu thức sau

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6) A = $\frac{1}{5+2\sqrt{3}} + \frac{1}{5-2\sqrt{3}}$

8) A = $\frac{5-2\sqrt{5}}{\sqrt{5-2}} - \sqrt{6-2\sqrt{5}}$

10) A = $\frac{\sqrt{35-\sqrt{7}} + 12}{\sqrt{5-1}} + \frac{1}{\sqrt{7-1}}$

12) A = $\frac{27-3\sqrt{2}}{\sqrt{3-\sqrt{2}}} - 6\frac{1}{3+\sqrt{3}}$

14) A = $\frac{\sqrt{6-\sqrt{3}}}{\sqrt{2}-1} - \sqrt{(1-\sqrt{3})^2}$

16) A = $\frac{5+2\sqrt{5}}{\sqrt{5}} + \sqrt{(3-\sqrt{5})^2}$

18)