定义域x,0定义域x,0
值域为R值域为R
在R上递增在R上递减
函数图象都过函数图象都过定点
定点(1,0)(1,0)
(三)幂函数
,(a,R)1、幂函数定义:
一般地,形如的函数称为幂函数,其中y,x
为常数(
2、幂函数性质归纳(
-7-
(1)所有的幂函数在(0,+?
)都有定义并且图象都过点(1,1);
,0
(2)时,幂函数的图象通过原点,并且在区间上是增函数(特[0,,,)
,10,,,1别地,当时,幂函数的图象下凸;当时,幂函数的图象上
凸;
,0(3)时,幂函数的图象在区间上是减函数(在第一象限内,(0,,,)
当从右边趋向原点时,图象在轴右方无限地逼近轴正半轴,当趋yyxx
时,图象在轴上方无限地逼近轴正半轴(于xx,,
例题:
x1.已知a>0,a0,函数y=a与y=log(-x)的图象只能是()a
2.若函数在区间上的最大值是最小值的3倍,则a=[a,2a]f(x),logx(0,a,1)a
1,x3.已知,
(1)求的定义域
(2)求使的的取值范围xfx()fx()0,fxaa()log(01),,,且a1,x
第三章函数的应用
一、方程的根与函数的零点
1、函数零点的概念:
对于函数,把使成立的实数xy,f(x)(x,D)f(x),0叫做函数的零点。
y,f(x)(x,D)
2、函数零点的意义:
函数的零点就是方程实数根,亦即函y,f(x)f(x),0数的图象与轴交点的横坐标。
xy,f(x)
即:
方程有实数根函数的图象与轴有交点函数xf(x),0y,f(x),,
有零点(y,f(x)
3、函数零点的求法:
1(代数法)求方程的实数根;f(x),0?
2(几何法)对于不能用求根公式的方程,可以将它与函数的y,f(x)?
图象联系起来,并利用函数的性质找出零点(
4、二次函数的零点:
2二次函数(y,ax,bx,c(a,0)
2ax,bx,c,0x
(1)?
,,方程有两不等实根,二次函数的图象与轴有两个交点,二次函数有两个零点(
2ax,bx,c,0x
(2)?
,,方程有两相等实根,二次函数的图象与轴有一个交点,二次函数有一个二重零点或二阶零点(
2ax,bx,c,0x(3)?
,,方程无实根,二次函数的图象与轴无交
点,二次函数无零点(
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(英文版)
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