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圆是轴对称图形,经过圆心的任意一条直线都是它的对称轴,于是就有了垂直于弦的直径的性质:垂直于弦的直径平分这条弦,并且平分弦所对的两条弧,即垂径定理.在垂径定理(推论)中,一是隐含着一条直线;二是该直线具有以下性质:(1)经过圆心,(2)垂直于弦,(3)平分这条弦,(4)平分这条弦所对的劣弧,(5)平分这条弦所对的优弧.具备其中任意两个条件,那么就可得到
The circle is an axisymmetric figure, and any straight line passing through the center of the circle is its axis of symmetry, so that there is a perpendicularity to the diameter of the string: bisects the string perpendicular to the diameter of the string and bisects the two arcs , That is, the law of the drop diameter. In the theorem of the drop (reasoning), one implies a straight line; second, the straight line has the following properties: (1) (4) bisects the inferior arc to which the string is directed, (5) bisects the superior arc to which the string corresponds, and with any two of these conditions, then