Răspuns:
a) [tex] x=\frac{1}{2}\left( \frac{(6\sqrt 3)(3\sqrt 3)}{15\sqrt 3}-\frac{4\cdot 5}{15\sqrt 3}-\frac{8\sqrt 3}{15\sqrt 3}\right) = \frac{1}{2}\cdot \frac{54-20-24}{15\sqrt 3}=\frac{10}{30\sqrt 3}=\frac{1}{3\sqrt 3}=\frac{\sqrt 3}{9}[/tex].
b) [tex] y= (-2\sqrt 3)^3 + (-\sqrt 3)^5 = -8\cdot 3\sqrt 3 - 9\sqrt 3 = -33\sqrt 3 [/tex]
[tex]x:y^{-1}=x\cdot y = \frac{\sqrt 3}{9}\cdot (-33\sqrt 3)=\frac{-33\cdot 3}{9}=-11\in\mathbb Z[/tex].
