1.连接O1,∵ A在圆上∴O1A是圆O1的半径
∵O1C是直径,所以角O1AC=90°,即O1A⊥AC
∴AC是切线
2.CE?+2CE X O1E =CE×(CE+2 O1E )=CE×(O2C+O1E)=CE×(O2C+O1A)= AC?