市级公开课演示课件—2016人教版高中数学必须修读12-2-2对数函数和其性质第一课时[共31张PPT].ppt

* * * 高中数学必修1 * 2.2.2 对数函数及其性质 第一课时 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. 思考：北京青年报曾报道：潮白河底挖出冰冻古树可能是山杨，专家经过检测可推断树的埋藏时间。你知道专家是根据什么推断树的埋藏时间的吗？ Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 举例：湖南长沙马王堆汉墓女尸出土时碳14的残余量约占原始含量的76．7％．试推算马王堆古墓的年代． 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. 　　一般地，我们把函数___________________叫 做对数函数，其中x是自变量，函数的定义域是 _____________ 探究1：对数函数的定义 y=logax(a0,且a≠1) （0，+∞）． Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 思考:对数函数的解析式具有什么样的结构特征呢？ 提示：对数函数的解析式具有以下三个特征： (1)底数a为大于0且不等于1的常数，不含有自变量x； (2)真数位置是自变量x，且x的系数是1； (3)logax的系数是1. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 思考:对数函数的定义域为何是（0，+∞）？ 提示：对数的真数要求大于0 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 探究2：对数函数的图象 对数函数作为一类重要的函数模型，要全方位把握它，不仅要知道它的函数解析式，更要知道它的函数图象。俗话说：“数缺形时少直观，形缺数时难入微”。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. （1）作y=log2x的图象 … … 列表 作图步骤: ①列表, ②描点, ③用平滑曲线连接. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 描点 连线 2 1 -1 -2 2 4 O y x 3 1 Evaluation only. Created with A