江蘇省泰興市新市初級(jí)中學(xué)七年級(jí)數(shù)學(xué)上冊(cè) 24 絕對(duì)值與相反數(shù)課件1 新版蘇科版

1、2.4,絕對(duì)值與相反數(shù),1,小明家在學(xué)校正西方,3 km,處，小麗家在學(xué),校正東方,2 km,處，假如他們步行的速度相同,誰先到學(xué)校？為什么,你會(huì)用數(shù)軸上的點(diǎn)表示學(xué)校、小明家、小,麗家的位置嗎,小明家,學(xué)校,小麗家,A,O,B,3,2,1,畫數(shù)軸，用數(shù)軸的原點(diǎn),O,表示學(xué)校的位置,規(guī)定向東為正，數(shù)軸上的,1,個(gè)單位長度表示,1,km,2,設(shè)點(diǎn),A,點(diǎn),B,分別表示小明家、小麗家，則點(diǎn),A,在原點(diǎn),O,左側(cè)且到原點(diǎn),O,的距離為,3,個(gè)單位長度,點(diǎn),B,在原點(diǎn),O,右側(cè)且到原點(diǎn),O,的距離為,2,個(gè)單位長,度,0,5,4,3,2,1,2,3,4,5,1,數(shù)軸上表示一個(gè)數(shù)的點(diǎn)與原點(diǎn)的距離,叫做這個(gè)

2、數(shù)的,絕對(duì)值,A,O,B,3,2,0,5,4,3,2,1,2,3,4,5,1,請(qǐng)你結(jié)合數(shù)軸，根據(jù)定義說出,3,2,0,的絕對(duì)值,你能說出數(shù)軸上的點(diǎn),A,B,C,D,E,所表,示的數(shù)的絕對(duì)值嗎,點(diǎn),A,表示的數(shù),5,的絕對(duì)值為,5,點(diǎn),B,表示的數(shù),3.5,的絕對(duì)值為,3.5,點(diǎn),C,表示的數(shù),1,的絕對(duì)值為,1,點(diǎn),D,表示的數(shù),2.5,的絕對(duì)值為,2.5,點(diǎn),E,表示的數(shù),5,的絕對(duì)值為,5,有理數(shù)的絕對(duì)值的求法,歸納,1,畫數(shù)軸,標(biāo)出有理數(shù)所在,點(diǎn)，得到點(diǎn)到原點(diǎn)的距離,2,求得有理數(shù)的絕對(duì)值,有理數(shù),絕對(duì)值,點(diǎn),距離,例,1,求,4,3.5,的絕對(duì)值,3.5,4,0,5,4,3,2,1,2

3、,3,4,5,1,因?yàn)辄c(diǎn),A,與原點(diǎn)的距離是,4,所以,4,的絕對(duì)值是,4,因?yàn)辄c(diǎn),B,與原點(diǎn)的距離是,3.5,所以,3.5,的絕對(duì)值是,3.5,解：在數(shù)軸上分別畫出表示,4,3.5,的點(diǎn),A,點(diǎn),B,B,A,通常，我們將數(shù),a,的絕對(duì)值記為,a,例如,4,的絕對(duì)值記為,4,3.5,的絕對(duì)值記為,3.5,例,2,已知一個(gè)數(shù)的絕對(duì)值是,求這個(gè)數(shù),2,5,解：數(shù)軸上到原點(diǎn)的距離是,的點(diǎn)有,2,個(gè)，它們,分別是點(diǎn),A,和點(diǎn),B,2,5,0,5,4,3,2,1,2,3,4,5,1,2,5,2,5,因?yàn)辄c(diǎn),A,點(diǎn),B,表示的數(shù)分別是,所以絕對(duì)值是,的數(shù)有,2,個(gè)，它們是,2,5,2,5,2,5,2,5,

4、2,5,B,A,例,3,比較,3,與,6,的絕對(duì)值的大小,3,5,4,3,2,1,0,6,6,解,因?yàn)?3,6,3,6,所以,3,即,3,的絕對(duì)值,小于,6,的絕對(duì)值,例,4,回答下列問題,1,說出,表示的意義,2,1,1,2,到原點(diǎn)距離為,3,的數(shù)是,3,絕對(duì)值為,3,的數(shù)是,4,絕對(duì)值為,3,的數(shù)是,5.,任何數(shù)的絕對(duì)值都是正數(shù)”的說法對(duì),嗎,任何一個(gè)數(shù)的絕對(duì)值一定是非負(fù)數(shù),例,5,計(jì)算,1,24,5,2,24,5,3,24,5,4,24,5,2,5,0,4,0,2,3,5,_,5,_,2,3,_,4,0,_,0,_,5,_,2,1,1,在數(shù)軸上畫出表示下列各數(shù)的點(diǎn),2,填空,2,已知一個(gè)數(shù)的絕對(duì)值是,2,求這個(gè)數(shù),5,2,3,0.4,0,5,2,4,1,4,3,3,2,3,1,4,4,3,2,2,1,3,2,1,3,計(jì)算,課堂小結(jié),談?wù)勀氵@一節(jié)課有哪些收獲,7,絕對(duì)值小于,4.5,的整數(shù)是,10,絕對(duì)值大于,1,且小于,5,的整數(shù)有,_,個(gè),它們是,9,絕對(duì)值不大于,3,的非負(fù)整數(shù)是,_,6,絕對(duì)值最小的數(shù)是,8,