题目

（本小题满分9分）已知⊙与⊙相交于、两点，点在⊙上，为⊙上一点（不与，，重合），直线与⊙交于另一点。（1）如图（8），若是⊙的直径，求证：；（2）如图(9)，若是⊙外一点，求证：；（3）如图（10），若是⊙内一点，判断（2）中的结论是否成立。 答案：证明：（1）如图（一），连接，∵为⊙的直径     ∴∴为⊙的直径     ∴在上又，为的中点∴△是以为底边的等腰三角形∴····················································································· （3分）（2）如图（二），连接，并延长交⊙与点，连∵四边形内接于⊙   ∴又∵               ∴∴又为⊙的直径          ∴∴···················································································· （3分）（3）如图（三），连接，并延长交⊙与点，连∵        又∴ ∴           又∴···················································································· （3分）解析:略

查看本题答案和解析