1.2.4绝对值第1课时01234-1-2-3大象距原点多远?两只小狗分别距原点多远?Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
1、理解绝对值的概念及其几何意义.2、会求一个数(不涉及字母)的绝对值.3、会求绝对值已知的数.4、了解绝对值的非负性,并能用其非负性解决相关问题.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
1.什么叫做相反数?2.你能找出互为相反数的两个数在数轴上表示的点的共同特点吗?Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
01234-1-2-3大象距原点多远?两只小狗分别距原点多远?Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
一般地,数轴上表示数a的点与原点的距离叫做数a的绝对值.想一想互为相反数的两个数的绝对值有什么关系?想一想这里的数a可以表示什么样的数?这里的数a可以是正数,负数和0.答:一对相反数虽然分别在原点两边,但它们到原点的距离是相等的.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
绝对值的表示数a的绝对值,记作:|a|.在数轴上表示-5的点与原点的距离是5,即-5的绝对值是5,记作:|-5|=5.的绝对值是,记作:Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
例1:求下列各数的绝对值.-19, ,0,-2.3,+0.56,-6,+6, .【解析】-19的绝对值是19,即|-19|=19;的绝对值是 ,即| |= ;0的绝对值是0,即|0|=0;Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
-2.3的绝对值是2.3,即|-2.3|=2.3;+0.56的绝对值是0.56,即|+0.56|=0.56;-6的绝对值是6,即|-6|=6;+6的绝对值是6,即|+6|=6;的绝对值是 ,即| |= ;Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
︱9︱=︱2.5︱=︱0︱=︱-2.5︱=︱-9︱=例2:求下列各数的值.92.52.590正数的绝对值是它本身负数的绝对值是它的相反数0的绝对值是0议一议:上述各数的绝对值与这些数本身有什么关系?正数的绝对值是它本身;负数的绝对值是它的相反数;0的绝对值是0.绝对值的代数意义Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
正数的绝对值是它本身小组之间讨论一下:(1)当a是正数时,|a|=____;(2)当a是负数时,|a|=__;(3)当a=0时,|a|=___.a-a00的绝对值是0负数的绝对值是它的相反数Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
1、说出下列各式的值2、求下列各数的绝对值9,-9,-3.9,3.9,,,0.答案:1.260答案:993.93.90Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
3、化简55-5-50.3Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
1、判断:(1)一个数的绝对值是2,则这个数是2()(2)|5|=|-5|() (3)|-0.3|=|0.3|()(4)|3|>0()(5)|-1.4|>0()(6)有理数的绝对值一定是正数()(7)若a=b,则|a|=|b|()(8)若|a|=|b|,则a=b()(9)若|a|=-a,则a必为负数()(10)互为相反数的两个数的绝对值相等()××××√√√√√√Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
(1)一个数的绝对值是7,则这个数是______.(2)满足︱x︱≤3的所有整数是.(3)绝对值大于2并且不大于5的负整数有.(4)如果,则a=_____,b=_____.(5)己知x=30,y=-4,则2、填空Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
(7)已知有理数a在数轴上对应的点如图所示:则|a|=________a0(8)如果一个数的绝对值等于3.25,则这个数是___(10)如果|x-1|=2,则x=______.(9)如果a的相反数是-0.74,那么|a|=___________83375.0(6)=-+计算:÷Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
3、(2010·鄂尔多斯中考)如果与1互为相反数,则︱a︱等于().A.2B.-2C.1D.-1【解析】选C.1的相反数是-1,︱-1︱=1.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
4、(2010·邵阳中考)―|―3|=()A.―3B.―C.D.3【解析】选A.︱-3︱=3,-︱-3︱=-3.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
5、已知︱x︱=6,︱y︱=4,并且x>y,求x+y的值;6、根据绝对值的意义,思考:(2)如果=1,那么a0.(2)如果a<0,那么-︱a︱=.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
绝对值数轴上表示数a的点与原点的距离(1)如果a>0,那么|a|=a(2)如果a<0,那么|a|=-a(3)如果a=0,那么|a|=0几何意义代数意义绝对值的非负性Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
努力向前,默默耕耘,机会和成功必属于最坚韧的奋斗者.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.