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八年级数学解答题一般
题目
如图,已知ABC\triangle ABCDCE\triangle DCE均是等边三角形,点BB,CC,EE在同一条直线上,AEAEBDBD相交于点OO,AEAECDCD交于点GG,ACACBDBD相交于点FF,连接OCOC,FGFG,则下列结论:①AG=BFAG=BF;②FGFGBE;BE;DF=DEDF=DE;④DOE=60\angle DOE=60^{\circ};⑤BOC=EOC\angle BOC=\angle EOC,其中正确的结论有____.
知识点:全等三角形的判定、等边三角形的性质、相似三角形的性质I、相似三角形的判定与性质章节:未标注

答案与解析

答案

ABC\because \triangle ABCDCE\triangle DCE均是等边三角形,
BC=AC\therefore BC=ACCD=CECD=CEACB=ECD=60\angle ACB=\angle ECD=60^{\circ}
ACB+ACD=ACD+ECD\therefore \angle ACB+\angle ACD=\angle ACD+\angle ECDACD=60\angle ACD=60^{\circ}
BCD\therefore \triangle BCDACE(SAS)\triangle ACE\left(SAS\right)
AE=BD\therefore AE=BD
CBD=CAE\angle CBD=\angle CAE
BCA=ACG=60\because \angle BCA=\angle ACG=60^{\circ}AC=BCAC=BC
BCF\therefore \triangle BCFACG(ASA)\triangle ACG\left(ASA\right)
AG=BF\therefore AG=BF(①正确)(①正确)
同理:DFC\triangle DFCEGC(ASA)\triangle EGC\left(ASA\right)
CF=CG\therefore CF=CG
CFG\therefore \triangle CFG是等边三角形,
CFG=FCB=60\therefore \angle CFG=\angle FCB=60^{\circ}
FG\therefore FGBE,(②正确)BE,(②正确)
DFCDFCGCE\triangle GCE
{FDC=GECDCF=ECGCF=CG\left\{\begin{array}{l}{∠FDC=∠GEC}\\{∠DCF=∠ECG}\\{CF=CG}\end{array}\right.
DFC\therefore \triangle DFCGCE(AAS)\triangle GCE\left(AAS\right)
DF=EG\therefore DF=EGDC=CEDC=CE(③不正确)(③不正确)
DOE=OBE+OEB\because \angle DOE=\angle OBE+\angle OEBOBE=OAC\angle OBE=\angle OAC
DOE=OAC+OEB\therefore \angle DOE=\angle OAC+\angle OEB
DOE=ACB\therefore \angle DOE=\angle ACB
ACB=60\because \angle ACB=60^{\circ}
DOE=60\therefore \angle DOE=60^{\circ},(④正确)
CCCMAECM\bot AEMMCNBDCN\bot BDNN

BCD\because \triangle BCDACE(ASA)\triangle ACE\left(ASA\right)
BDC=AEC\therefore \angle BDC=\angle AEC
CD=CE\because CD=CECND=CMA=90\angle CND=\angle CMA=90^{\circ}
CDN\therefore \triangle CDNCEM\triangle CEM
CM=CN\therefore CM=CN
CMAE\because CM\bot AECNBDCN\bot BD
RtOCN\therefore \triangle Rt\triangle OCNRtOCM(HL)Rt\triangle OCM\left(HL\right)
BOC=EOC\therefore \angle BOC=\angle EOC
\therefore⑤正确;
故答案为:①②④⑤.

解析

ABC\because \triangle ABCDCE\triangle DCE均是等边三角形,
BC=AC\therefore BC=ACCD=CECD=CEACB=ECD=60\angle ACB=\angle ECD=60^{\circ}
ACB+ACD=ACD+ECD\therefore \angle ACB+\angle ACD=\angle ACD+\angle ECDACD=60\angle ACD=60^{\circ}
BCD\therefore \triangle BCDACE(SAS)\triangle ACE\left(SAS\right)
AE=BD\therefore AE=BD
CBD=CAE\angle CBD=\angle CAE
BCA=ACG=60\because \angle BCA=\angle ACG=60^{\circ}AC=BCAC=BC
BCF\therefore \triangle BCFACG(ASA)\triangle ACG\left(ASA\right)
AG=BF\therefore AG=BF(①正确)(①正确)
同理:DFC\triangle DFCEGC(ASA)\triangle EGC\left(ASA\right)
CF=CG\therefore CF=CG
CFG\therefore \triangle CFG是等边三角形,
CFG=FCB=60\therefore \angle CFG=\angle FCB=60^{\circ}
FG\therefore FGBE,(②正确)BE,(②正确)
DFCDFCGCE\triangle GCE
{FDC=GECDCF=ECGCF=CG\left\{\begin{array}{l}{∠FDC=∠GEC}\\{∠DCF=∠ECG}\\{CF=CG}\end{array}\right.
DFC\therefore \triangle DFCGCE(AAS)\triangle GCE\left(AAS\right)
DF=EG\therefore DF=EGDC=CEDC=CE(③不正确)(③不正确)
DOE=OBE+OEB\because \angle DOE=\angle OBE+\angle OEBOBE=OAC\angle OBE=\angle OAC
DOE=OAC+OEB\therefore \angle DOE=\angle OAC+\angle OEB
DOE=ACB\therefore \angle DOE=\angle ACB
ACB=60\because \angle ACB=60^{\circ}
DOE=60\therefore \angle DOE=60^{\circ},(④正确)
CCCMAECM\bot AEMMCNBDCN\bot BDNN

BCD\because \triangle BCDACE(ASA)\triangle ACE\left(ASA\right)
BDC=AEC\therefore \angle BDC=\angle AEC
CD=CE\because CD=CECND=CMA=90\angle CND=\angle CMA=90^{\circ}
CDN\therefore \triangle CDNCEM\triangle CEM
CM=CN\therefore CM=CN
CMAE\because CM\bot AECNBDCN\bot BD
RtOCN\therefore \triangle Rt\triangle OCNRtOCM(HL)Rt\triangle OCM\left(HL\right)
BOC=EOC\therefore \angle BOC=\angle EOC
\therefore⑤正确;
故答案为:①②④⑤.

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