1. Cho $A=\frac{1+xy}{x+y}-\frac{1-xy}{x-y}$ biết $x=\sqrt{4+\sqrt{8}}*\sqrt{2+\sqrt{2+\sqrt{2}}}*\sqrt{2-\sqrt{2+\sqrt{2}}}$ ; $y=\frac{3\sqrt{8}-2\sqrt{2}+\sqrt{20}}{3\sqrt{18}-2\sqrt{27}+\sqrt{45}}$
2.So sánh: $C=\sqrt{5}(\sqrt{6}+1):\sqrt{\frac{2\sqrt{3}+2}{2\sqrt{3}-2}}$
$D=\sqrt{29}$
3. Cho $E=x^{2}-3x\sqrt{y}+2y$. Tính E biết $x=\frac{1}{\sqrt{5}-2}; y=\frac{1}{9+4\sqrt{5}}$
