źródło:
r=\frac{2P}{a+b+c}=\frac{2*25\sqrt{3}}{10(2+\sqrt{3})}=\frac{50\sqrt{3}}{10(2+\sqrt{3})}=\frac{5\sqrt{3}}{2+\sqrt{3}}=\frac{5\sqrt{3}(2-\sqrt{3})}{(2+\sqrt{3})(2-\sqrt{3})}=\frac{10\sqrt{3}-15}{4-3}=10\sqrt{3}-15}