求线段的比.ppt

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,INTEL CONFIDENTIAL,*,第二十五章图形的相似,求线段的比,情景导入,相似三角形中有一些基本图形,A,型图和,X,型图，,如果能识别这些基本图形，,并把它们从复杂的,图形中挖掘出来,，问题就迎刃而解了。,重点解析,1.,文字语言,:,2.,图形语言,:,3.,模型语言,:,4.,符号语言,:,A,D,E,B,C,平行于三角形一边的直线截其它两边（或两边的延长线），所得的对应线段成比例。且截得三角形与原三角形相似。,DEBC,字母 型,A,字母 型,X,F,A,B,C,D,AFBC,F,过点,D,作,DFAC,交,BE,于点,F,则,BFDBEC,AEG DFG,1,、如图，,D,为,ABC,的,BC,边的中点，,E,为,AC,边上的一点，,AC=3CE,，,BE,和,AD,交于,G,点，则,AG,：,GD=,（）,A,2 B,3 C,3,或,4 D,4,解法一,F,过点,D,作,DFBE,交,AC,于点,F,则,CDFCBE,AEG AFD,1,、如图，,D,为,ABC,的,BC,边的中点，,E,为,AC,边上的一点，,AC=3CE,，,BE,和,AD,交于,G,点，则,AG,：,GD=,（）,A,2 B,3 C,3,或,4 D,4,解法二,过线段的中点作平行线，是常作的辅助线。,A,C,B,F,E,D,G,解法一,过点,E,作,EGAC,交,BC,于点,G,则,BEGBDC,FEG FAC,2,、如图：在,ABC,中，点,D,在,AC,上，且,AD,：,DC,=1,：,2,，连接,BD,，,E,为,BD,中点，延长,AE,交,BC,于,点,F,，则,BF,：,FC=,A,1,：,4 B,1,：,3 C,2,：,5 D,3,：,8,A,C,B,F,E,D,G,解法二,过点,E,作,EGBC,交,AC,于点,G,则,DEGDBC,AEG AFC,2,、如图：在,ABC,中，点,D,在,AC,上，且,AD,：,DC,=1,：,2,，连接,BD,，,E,为,BD,中点，延长,AE,交,BC,于,点,F,，则,BF,：,FC=,A,1,：,4 B,1,：,3 C,2,：,5 D,3,：,8,A,C,B,F,E,D,G,过点,D,作,DGAF,交,BC,于点,G,则,BEFBDG,CDG CAF,2,、如图：在,ABC,中，点,D,在,AC,上，且,AD,：,DC,=1,：,2,，连接,BD,，,E,为,BD,中点，延长,AE,交,BC,于,点,F,，则,BF,：,FC=,A,1,：,4 B,1,：,3 C,2,：,5 D,3,：,8,解法三,A,C,B,F,E,D,G,解法四,过点,D,作,DGBC,交,AE,于点,G,则,BEFDEG,AGD AFC,2,、如图：在,ABC,中，点,D,在,AC,上，且,AD,：,DC,=1,：,2,，连接,BD,，,E,为,BD,中点，延长,AE,交,BC,于,点,F,，则,BF,：,FC=,A,1,：,4 B,1,：,3 C,2,：,5 D,3,：,8,过线段的中点或端点作平行线，是常作的辅助线。,亮点概述,过线段的中点或端点作平行线，是常作的辅助线。,平行线分线段成比例定理是研究相似形最重要、最基本的理论基础,而字母,A,型、字母,X,型又是解决相似三角形有关计算和证明的模具,