a=6cm
R=\frac{2}{3}h=\frac{2}{3}*\frac{a\sqrt3}{2}=\frac{6\sqrt3}{3}=2\sqrt3(cm)
P=\pi R^2=\pi(2\sqrt3)^2=12\pi (cm^2)
Odp A
Zad. 14
sin\alpha=\frac{2}{3}
sin^2\alpha+cos^2\alpha=1
\frac{4}{9}+cos^2\alpha=1
cos^2\alpha=1-\frac{4}{9}
cos\alpha=\sqrt{\frac{5}{9}}=\frac{\sqrt5}{3}
Odp. C.