23/01/10 08:39:34.53 JLU3lsi9.net
アークサインを使ってよければ
do=pi/180
BD=6
CD=4
R=BD/sin(120*do)/2
BDC=pi-60*do-asin(CD/(2*R))
BC=sin(pi-60*do-asin(CD/(2*R)))*2*R
EDC=BDC
DEC=pi-30*do-EDC
CE/sin(EDC)=CD/sin(DEC)
CE=CD/sin(DEC)*sin(EDC)
CE
> CE
[1] 4.385505
> 8*sqrt(2)-4*sqrt(3)
[1] 4.385505