2.2.2对数函数及其性质(第1课时)课前复习:1、指数式与对数式的互化xaNlogaxN01a图象性质1a定义域值域1xOy1xOyRxya(0,+)(0,1)过定点恒001=xya即时,恒有R在上是增函数001xy当时,01>>xy当时,R在上是减函数01>xy当时,01><0(3)21148>0xxx由题意可得1>211,<<212<2xxxxx解得即且1<<212xxx函数的定义域是且()(4,2),(2)fxf例2已知对数函数的图象过点求。()log(0,1)aafxxa解:设该对数函数为且(4,2)2log4,a函数图象过点,Q24a,2()log(0).fxxx即所求对数函数为012aaa且,Q2(2)log21f二、例题讲解三、对数函数图象与性质在坐标系中画出下面两个函数的图象2(1)logyx解:(1)列表如下{|>0}xx定义域:x0.51248-101232logyx-11345678910xyO122logyx23在坐标系中画出下面两个函数的图象2(1)logyx解:(1)列表如下3(2)logyx-11345678910xyO122logyxx13927-101233logyx133logyxx0.51248-101232logyx2logyx3logyx12logyx13logyx观察下列四个函数的图象,能否总结出其图象特征?结论:底大图低(x>1部分)三、对数函数图象与性质图象定义域值域性质定点单调性a>10<a<1oyx(1,0))1(logaxyaoyx(1,0))10(logaxya),0(R过定点(1,0),即x=1时,y=loga1=0在上是增函数),0(在上是减函数),0(当x>1时,当00y<0当x>1时,当00logayx2logyx3log...