作圆的内接正八边形zuo yuan de neijiezhengbabianxing
作法❶在⊙O内作直径AE⊥CG（如图）;
❷平分AC,CE,EG,GA各弧于B,D,F,H;
❸顺次连结A,B,C,D,E,F,G,H.则八边形ABCDEFGH就是所求的圆内接正八边形.
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