[Toán 9] tính

N

nttthn_97

3
$\frac{\sqrt{10}+2\sqrt{10}}{\sqrt{5}+ \sqrt{2}}+ \frac{8}{1-\sqrt{5}}$

$=\frac{\sqrt{20}(\sqrt{5}+ \sqrt{2})}{\sqrt{5}+\sqrt{2}}+\frac{8(1+\sqrt{5})}{-4}$

$=2\sqrt{5}-2-2\sqrt{5}=-2$

4

$=\frac{2(\sqrt{8}+\sqrt{3}}{\sqrt{8}+\sqrt{3}}+ \frac{\sqrt{5}+\sqrt{27}}{\sqrt{6}(\sqrt{5}+\sqrt{27})}=\frac{3}{\sqrt{6}}$
 
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