2则圆中阴影部分面积为
A20cm2B10cm2C25cm2D16cm24如图△ABC沿直线BC方向向右移了3厘米得△FDE且BC6厘米∠B40°1求BE的长2求∠FDB的度数3找出图中相等的线段不另添加线段4找出图中互相平行的线段不另添加线段
答案解析1相交线【跟踪训练】1【解析】选C根据对顶角的定义可知图中只有第二个是对顶角其他都不是2【解析】选B∵∠EOC∶∠EOD2∶3∴∠EOC180°×72°∵OA平分∠EOC∴∠AOC∠EOC×72°36°∴∠BOD∠AOC36°3【解析】选C可知∠FOB∠1∵∠2∠3∠FOB180°∴∠1∠2∠3180°【跟踪训练】1【解析】选D∵EO⊥CD∴∠EOD90°又∵∠AOE∠EOD∠BOD180°∠AOE36°∴∠BOD54°2【解析】选D∵∠AOC35°∴∠BOD35°∵EO⊥AB∴∠EOB90°∴∠EOD∠EOB∠BOD90°35°125°3【解析】选B由OE⊥AB得∠AOE90°由对顶角相等得∠AOC∠BOD70°由OF平分∠AOC得∠AOF∠AOC35°由角的和差得∠EOF∠AOF∠AOE35°90°125°4【解析】1∵OE平分∠BOC∠BOE70°∴∠BOC2∠BOE140°∴∠AOC180°140°40°又∠COF90°∴∠AOF90°40°50°
f2∵∠BOD∶∠BOE1∶2OE平分∠BOC∴∠BOD∶∠BOE∶∠EOC1∶2∶2∴∠BOD36°∴∠AOC36°又∵∠COF90°∴∠AOF90°36°54°5【解析】1∵∠AOM90°OC平分∠AOM∴∠AOC∠AOM×90°45°∵∠AOC∠AOD180°∴∠AOD180°∠AOC180°45°135°2∵∠BOC4∠NOB∴设∠NOBx°∠BOC4x°∴∠CON∠COB∠BON4x°x°3x°∵OM平分∠CON∴∠COM∠MON∠CONx°∵∠BOMx°x°90°∴x°36°∴∠MONx°×36°54°2平行线的性质与判定【跟踪训练】1【解析】选A∵AC∥BD∴∠CAB∠DBA180°∵AOBO分别是∠BAC∠ABD的平分线∴∠BAO∠CAB∠ABO∠DBA∴∠BAO∠ABO∠CAB∠DBA90°2【解析】选B∵AB∥CD∴∠ABC∠C40°又∵CB平分∠ABD∴∠ABD2∠ABC80°又∵AB∥CD∴∠ABD∠D180°∴∠D100°3【解析】选BB中∠1与∠2是内错角∵∠1∠2根据内错角相等两直线平行可推出AB∥CD4【解析】选B∵AB∥CD∠158°∴∠EFD58°又∵FG平分∠EFD∴∠GFD∠EFD29°∵AB∥CD∴∠FGB∠GFD180°∴∠FGB151°5【解析】选C选项A中∠1∠2时根据内错角相等两直线平行可知a∥b选项B中∠1∠2且∠3∠4且∠1∠2180°且∠3∠4180°所以∠1∠290°且∠3∠490°所以a∥b选项D中OAOBOCOD故四边形ADBC是平行四边形所以a∥b选项C中∠1∠2不能确定ab平行6【解析】选B延长ED交BC于F
f∵AB∥DE∠ABC70°∴∠MFC∠B70°∵∠CDE140°∴∠FDC180°140°40°∴∠C∠MFC∠MDC70°40°30°7【解析】选CA、若ar