>>265
数値計算のコア部分は

# B(0,0) C(a,0) A(a1,a2)
c=AB=5
a=BC=6
b=AC=4
a1 = (a^2-b^2+c^2)/(2*a)
a2 = sqrt(c^2 - (a^2 - b^2 + c^2)^2/(4*a^2))
s=tan(atan2(a2,a1)/2)
t=tan(atan2(a2,a1-a))
BX=a*(sqrt(t^2+1)+1)/(s*t+sqrt(t^2+1)+1)
R=s*BX