《2012版中考数学精品课件含1011真题第二十七讲圆的认识2.pptVIP

【解析】选D.如图，此图形为轴对称图形，故BE＝DF＝4,所 以EF＝14,即圆的直径为14,连接MN，因为∠P＝90°，所以MN 为⊙O的直径，所以MN＝14,又B、C分别为MP、PN的中点，所 以BC为△MNP的中位线，所以BC＝ MN＝7,即菱形ABCD的边长 为7. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 6.(2011·绍兴中考)一条排水管截面如图 所示，已知排水管的截面圆半径OB=10， 截面圆圆心O到水面的距离OC是6，则水 面宽AB是( ) (A)16 (B)10 (C)8 (D)6 【解析】选A.由勾股定理可得BC=8，由垂径定理可得AB=2BC=16. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 缜密思考分类全面不漏解 圆中一条弦所对的弧有两条，圆内两条平行的弦与圆心的位置关系有两种情况，因此，在解决相关问题时，要缜密分析，全面思考，将可能出现的情况逐一进行分类，讨论解答，不要漏解. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 【例】(2011·凉山中考)如图，∠AOB=100°， 点C在⊙O上，且点C不与A、B重合，则∠ACB的 度数为( ) (A)50° (B)80°或50° (C)130° (D)50°或130° Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 【思路点拨】 【自主解答】选D.由圆周角与圆心角的关系可得，当点C在劣 弧 上时，∠ACB=130°,当点C在优弧 上时，∠ACB=50°. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. (2010·襄樊中考)已知⊙O的半径为13 cm，弦AB∥CD, AB=24 cm，CD=10 cm，则AB、CD之间的距离为( ) (A)17 cm (B)7 cm (C)12 cm (D)17 cm或7 cm Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. * Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 结合近几年中考试题分析，对圆的认识这 部分内容的考查主要有以下特点： 1.命题方式为圆的有关概念和性质,垂径定理及其应用,与圆有关的角的性质及其应用,在考查时主要以填空题、选择题的形式出现，不会有繁杂的证明题，取而代之的是简单的计算题和开放