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八年级数学填空题一般
题目
如图,在ABC\triangle ABC中,AB=ACAB=AC,BAC=90\angle BAC=90^{\circ},ADBCAD\bot BC于点DD,BEBE平分ABC\angle ABCACAC于点EE,交ADAD于点GG,过点AAAFBEAF\bot BE于点HH,交BCBC于点FF,下列结论:
AGE=AEG\angle AGE=\angle AEG
AE=DFAE=DF
GD+DC=ABGD+DC=AB
SABF=2SAFC+SAGES_{\triangle ABF}=2S_{\triangle AFC}+S_{\triangle AGE}
其中正确的是______.(填序号).(填序号)
知识点:线段垂直平分线的性质、全等三角形的性质、全等三角形的判定、直角三角形全等的判定、等腰三角形的性质、等腰三角形的判定定理、直角三角形的性质、三角形的面积章节:第13章 三角形 / 13.1 三角形的概念

答案与解析

答案

BE\because BE平分ABC\angle ABCACAC于点EE
ABG=CBG\therefore \angle ABG=\angle CBG
AFBE\because AF\bot BE
BAC=AHB=90\therefore \angle BAC=\angle AHB=90^{\circ}
ABG+AEG=CBG+BGD=90\therefore \angle ABG+\angle AEG=\angle CBG+\angle BGD=90^{\circ}
BGD=AEB\therefore \angle BGD=\angle AEB
AGE=BGD\because \angle AGE=\angle BGD
AGE=AEG\therefore \angle AGE=\angle AEG,故①正确;

如图,连接FGFG
ABH=FBH\because \angle ABH=\angle FBHAHB=FHB\angle AHB=\angle FHBBH=BHBH=BH
ABH\therefore \triangle ABHFBH(AAS)\triangle FBH\left(AAS\right)
AH=HF\therefore AH=HF
BH\therefore BH垂直平分AFAF
AG=FG\therefore AG=FG
AE=FG\therefore AE=FG
ADBC\because AD\bot BC
GDF=90\therefore \angle GDF=90^{\circ}
FG>DF\therefore FG \gt DF
AE>DF\therefore AE \gt DF,故②错误;
BH\because BH垂直平分AFAF
AB=BF\therefore AB=BF
ABG\therefore \triangle ABGFBG(SSS)\triangle FBG\left(SSS\right)
BFG=BAD=45\therefore \angle BFG=\angle BAD=45^{\circ}
DGF\therefore \triangle DGF是等腰直角三角形,
DF=DG\therefore DF=DG
BD=CD\because BD=CD
AB=BF=BD+DF=CD+DG\therefore AB=BF=BD+DF=CD+DG,故③正确;
AGE=AEG\because \angle AGE=\angle AEGAFEGAF\bot EG
GH=EH\therefore GH=EH
AH=FH\because AH=FHAHE=FHG\angle AHE=\angle FHG
AEH\therefore \triangle AEHFGH(SAS)\triangle FGH\left(SAS\right)
SAEG=SAFG\therefore S_{\triangle AEG}=S_{\triangle AFG}
AD=BD=CD\because AD=BD=CDDG=DFDG=DF
AG=CF\therefore AG=CF
AB=AC\because AB=ACBAD=C=45\angle BAD=\angle C=45^{\circ}
ABG\therefore \triangle ABGCAF(SAS)\triangle CAF\left(SAS\right)
SABG=SACF\therefore S_{\triangle ABG}=S_{\triangle ACF}
ABG\because \triangle ABGFBG\triangle FBG
SBGF=SACF\therefore S_{\triangle BGF}=S_{\triangle ACF}
SABF=SABG+SBFG+SAGF=2SAFC+SAGE\therefore S_{\triangle ABF}=S_{\triangle ABG}+S_{\triangle BFG}+S_{\triangle AGF}=2S_{\triangle AFC}+S_{\triangle AGE}.故④正确;
综上所述:正确的是①③④.
故答案为:①③④.

解析

BE\because BE平分ABC\angle ABCACAC于点EE
ABG=CBG\therefore \angle ABG=\angle CBG
AFBE\because AF\bot BE
BAC=AHB=90\therefore \angle BAC=\angle AHB=90^{\circ}
ABG+AEG=CBG+BGD=90\therefore \angle ABG+\angle AEG=\angle CBG+\angle BGD=90^{\circ}
BGD=AEB\therefore \angle BGD=\angle AEB
AGE=BGD\because \angle AGE=\angle BGD
AGE=AEG\therefore \angle AGE=\angle AEG,故①正确;

如图,连接FGFG
ABH=FBH\because \angle ABH=\angle FBHAHB=FHB\angle AHB=\angle FHBBH=BHBH=BH
ABH\therefore \triangle ABHFBH(AAS)\triangle FBH\left(AAS\right)
AH=HF\therefore AH=HF
BH\therefore BH垂直平分AFAF
AG=FG\therefore AG=FG
AE=FG\therefore AE=FG
ADBC\because AD\bot BC
GDF=90\therefore \angle GDF=90^{\circ}
FG>DF\therefore FG \gt DF
AE>DF\therefore AE \gt DF,故②错误;
BH\because BH垂直平分AFAF
AB=BF\therefore AB=BF
ABG\therefore \triangle ABGFBG(SSS)\triangle FBG\left(SSS\right)
BFG=BAD=45\therefore \angle BFG=\angle BAD=45^{\circ}
DGF\therefore \triangle DGF是等腰直角三角形,
DF=DG\therefore DF=DG
BD=CD\because BD=CD
AB=BF=BD+DF=CD+DG\therefore AB=BF=BD+DF=CD+DG,故③正确;
AGE=AEG\because \angle AGE=\angle AEGAFEGAF\bot EG
GH=EH\therefore GH=EH
AH=FH\because AH=FHAHE=FHG\angle AHE=\angle FHG
AEH\therefore \triangle AEHFGH(SAS)\triangle FGH\left(SAS\right)
SAEG=SAFG\therefore S_{\triangle AEG}=S_{\triangle AFG}
AD=BD=CD\because AD=BD=CDDG=DFDG=DF
AG=CF\therefore AG=CF
AB=AC\because AB=ACBAD=C=45\angle BAD=\angle C=45^{\circ}
ABG\therefore \triangle ABGCAF(SAS)\triangle CAF\left(SAS\right)
SABG=SACF\therefore S_{\triangle ABG}=S_{\triangle ACF}
ABG\because \triangle ABGFBG\triangle FBG
SBGF=SACF\therefore S_{\triangle BGF}=S_{\triangle ACF}
SABF=SABG+SBFG+SAGF=2SAFC+SAGE\therefore S_{\triangle ABF}=S_{\triangle ABG}+S_{\triangle BFG}+S_{\triangle AGF}=2S_{\triangle AFC}+S_{\triangle AGE}.故④正确;
综上所述:正确的是①③④.
故答案为:①③④.

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