căn bậc 2 + căn bậc 8 - căn bậc 32 (2 - căn bậc 5 ) ( 2 + căn bậc 5) 2 phần căn bậc 5 - 1 - 2 phần căn bậc 5 +1 2 nhân căn bậc 4 x - 8 - căn bậc 9 x - 18 = 3

$\sqrt{2\:}+\sqrt{8}-\sqrt{32}$

$=\sqrt{2}+2\sqrt{2}-4\sqrt{2}$

$=-\sqrt{2}$

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$\left(2-\sqrt{5}\right)\left(2+\sqrt{5}\right)$

$=2^2-\left(\sqrt{5}\right)^2$

$=-1$

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 $\dfrac{2}{\sqrt{5}-\:1}\:\:-\:\dfrac{2}{\sqrt{\:5\:}+1\:}$

$=\dfrac{\sqrt{5}+1}{2}-\dfrac{2}{\sqrt{5}+1}$

$=\dfrac{\sqrt{5}+1}{2}-\dfrac{\sqrt{5}-1}{2}$

$=\dfrac{\sqrt{5}+1-\left(\sqrt{5}-1\right)}{2}$

$=\dfrac{2}{2}$ $=1$

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$2\cdot \sqrt{\:4\:x\:-\:8}-\sqrt{\:9\:x\:-\:18}=3$

$⇔\sqrt{-2+x}=3$

$⇔-2+x=9$

$⇔x=11$

$\text{Vậy S = {11}}$