AC=6,BC=6√3
∠B=30° , AB=12 ，∠A=60°
OD=r , OB=2r , AB=3r
3r=12
r=4
(2)
△AOE是等边
∠EFA=30°
OH=2
HF=2√3,EF=4√3
S弓形EDF
=1/3S圆－S△EOF
=16π/3- 1/2*2*4√3
=16π/3- 4√3
