trójkąt prostokątny 30,60,90
a\sqrt{3}=30
BC=AD=a=\frac{30}{\sqrt{3}}=\frac{30\sqrt{3}}{\sqrt{3}*\sqrt{3}}=\frac{30\sqrt{3}}{3}=10\sqrt{3}
AB=2a=20\sqrt{3}
sin60=\frac{h}{BC}=\frac{h}{10\sqrt{3}}
\frac{\sqrt{3}}{2}=\frac{h}{10\sqrt{3}}
2h=30
h=15
(FB)^2=(BC)^2-h^2=(10\sqrt{3})^2-15^2=300-225=75
FB=\sqrt{75}=\sqrt{3*25}=5\sqrt{3}
CD=AB-2FB=20\sqrt{3}-2*5\sqrt{3}=10\sqrt{3}
OB=3*10\sqrt{3}+20\sqrt{3}=50\sqrt{3}