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28 a VA ROG dau coroana

28 A VA ROG Dau Coroana class=

Răspuns :

[tex]\frac{2}{\sqrt5+\sqrt3}+\frac{1}{\sqrt3+\sqrt2}+\frac{4}{\sqrt9+\sqrt5}=\\ \frac{2(\sqrt5-\sqrt3)}{(\sqrt5+\sqrt3)(\sqrt5-\sqrt3)}+\frac{\sqrt3-\sqrt2}{(\sqrt3+\sqrt2)(\sqrt3-\sqrt2)}+\frac{4(\sqrt9-5)}{(\sqrt9-\sqrt5)(\sqrt9+\sqrt5)}=\\ \frac{2(\sqrt5-\sqrt3)}{2}+\sqrt3-\sqrt2+\frac{4(\sqrt9-\sqrt5)}{4}=\\ \sqrt5-\sqrt3+\sqrt3-\sqrt2+3-\sqrt5=3-\sqrt2[/tex]