Question

如图,圆O为过A.B.C.D的圆,圆心在AD上,OC//AB.若AC=8AD:BC=5:3,求圆O的半径

Answer 1

角 OAC = 角OCA = 角CAB

所以弧 BC = 弧CD

所以连上CD的话,BC = CD

ACD是个直角三角形,又有AD:BC=5:3的条件,也就是AD:CD=5:3,所以这三边的比是 AD :AC :CD = 5 :4 :3 ,而AC = 8 所以AD = 10 ,半径是5