江苏省徐州市2019-2019年度第一学期八年级数学期中试卷
及评分
2016-2017学年度第一学期期中检测八年级数学期中答案一、选择
(每题3分,共24分)9.三角形的稳定性10.311.80°或50°12.∠B=∠C或DC=BD或∠CAD=∠BAD13.214.9.615.1516.110三、简答题∴ME=MF,∵N是EF的中点,∴MN⊥EF...........................6分19.每图2分20.(1)解:作出点P、Q分别得2分,用尺规作图不得分(2)∵262=CQ262=BQ522=BC...............7分∴222BCBQCQ=+,∴△CBQ是直角三角形.........8分21.证明:(1)∵△ABC为等边三角形,∴AB=AC,∠BAC=60°,...................................2分在△ABP和△ACQ中,,∴△ABP≌△ACQ(SAS),................................4分(2)∵△ABP≌△ACQ,∴∠BAP=∠CAQ,AP=AQ,∴△APQ是等腰三角形....................................6分∵∠BAP+∠CAP=60°,∴∠PAQ=∠CAP+∠CAQ=60°,∴等腰△APQ是等边三角形................................................8分22.(1)作图2分(要有作图痕迹)(2))设AE=xkm,∵C、D两村到E站的距离相等,∴DE=CE,即DE2=CE2,...3分由勾股定理,得152+x2=102+(25-x)2,.......................................5分x=10.故:E点应建在距A站10千米处...........................................6分23.(1)∵DM、EN分别垂直平分AC和BC,∴AM=CM,BN=CN,......................................................1分∴△CMN的周长=CM+MN+CN=AM+MN+BN=AB,..............................2分∵△CMN的周长为15cm,∴AB=15cm;............................................................3分(2)∵∠MFN=70°,∴∠MNF+∠NMF=180°-70°=110°,∵∠AMD=∠NMF,∠BNE=∠MNF,∴∠AMD+∠BNE=∠MNF+∠NMF=110°,∴∠A+∠B=90°-∠AMD+90°-∠BNE=180°-110°=70°,.......................4分∵AM=CM,BN=CN,∴∠A=∠ACM,∠B=∠BCN,..............................................5分∴∠MCN=180°-2(∠A+∠B)=180°-2×70°=40°..........................6分24.(1)5,................................................................1分EF=BE+CF∵BO平分∠ABC∴∠EBO=∠OBC∵EF∥BC∴∠EOB=∠OBC∴∠EOB=∠EBO∴EO=EB.......................................................2分同理FO=FC..............................................3分∴EF=EO+FO=BE+CF..............................................4分(2)2,△BEO,△CFO,EF=BE+CF........................................8分(3)2,.............................................................9分EF=BE—CF∵BO平分∠ABC∴∠EBO=∠OBC∵EF∥BC∴∠EOB=∠OBC∴∠EOB=∠EBO∴EO=EB...........................................10分同理FO=FC............................................11分∴EF=EO-FO=BE-CF............................................12分25.(1)在Rt△ABC中,222ABBCAC=+∴4=AC......................1分,........................................................................................∴............................................................................................在边BC∴.......................................∴..................................................