大圆半径R/小圆半径r=根号5:根号2
OC=OD=r
OA=OB=R
OE=CE=ED=1,解得OC=根号2倍的CE
AC+CE=1/2AB,AC=CE,
OE平方+AE平方=OA平方,OA=根号5倍的OE,
OE=CE所以R/r=根号5比根号2