Sc=EH²π=π,EH=1,AH:BH=1:2,AH+BH=2R,AH=2R/3,OH=R-AH=R/3,
EH垂直AB,OE=R,OE²=EH²+OH², R²-R²/9=π²,8R²/9=π² ,R²=9π²/8
So=4πR²=4π*9π²/8=9π³/2.
