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八年级数学填空题一般
题目
如图,在等腰RtABCRt\triangle ABC中,BAC=90\angle BAC=90^{\circ},DD,EEBCBC上两点,DAE=45\angle DAE=45^{\circ},FFABC\triangle ABC外一点,且BFBCBF\bot BC,AFAEAF\bot AE,则下列结论:①CE=BFCE=BF;②BD2+DE2=CE2BD^{2}+DE^{2}=CE^{2};③SADE=14ADEFS_{△ADE}=\frac{1}{4}AD•EF;④CE2+BE2=2AE2CE^{2}+BE^{2}=2AE^{2},其中正确的结论序号有______.
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

在等腰RtABCRt\triangle ABC中,BAC=90\angle BAC=90^{\circ}
AB=AC\therefore AB=AC
ABC=C=45\therefore \angle ABC=\angle C=45^{\circ}
FBBC\because FB\bot BC
FBC=90\therefore \angle FBC=90^{\circ}
ABF=45\therefore \angle ABF=45^{\circ}
C=ABF\therefore \angle C=\angle ABF
FAAE\because FA\bot AE
FAE=90\therefore \angle FAE=90^{\circ}
CAE=BAF=90BAE\therefore \angle CAE=\angle BAF=90^{\circ}-\angle BAE
CAE\triangle CAEBAF\triangle BAF中,
{C=ABFAC=ABCAE=BAF\left\{\begin{array}{l}{∠C=∠ABF}\\{AC=AB}\\{∠CAE=∠BAF}\end{array}\right.
CAE\therefore \triangle CAEBAF(ASA)\triangle BAF\left(ASA\right)
CE=BF\therefore CE=BFAE=AFAE=AF
故①正确;
如图,连接DFDF

DAE=45\because \angle DAE=45^{\circ}BAC=90\angle BAC=90^{\circ}
DAF=BAD+BAF=BAD+CAE=45\therefore \angle DAF=\angle BAD+\angle BAF=\angle BAD+\angle CAE=45^{\circ}
DAF=DAE\therefore \angle DAF=\angle DAE
DAF\triangle DAFDAE\triangle DAE中,
{AF=AEDAF=DAEAD=AD\left\{\begin{array}{l}{AF=AE}\\{∠DAF=∠DAE}\\{AD=AD}\end{array}\right.
DAF\therefore \triangle DAFDAE(SAS)\triangle DAE\left(SAS\right)
DF=DE\therefore DF=DE
BD2+BF2=DF2\because BD^{2}+BF^{2}=DF^{2}
BD2+CE2=DE2\therefore BD^{2}+CE^{2}=DE^{2}
故②错误;
如图,设EFEFADAD于点GG
AF=AE\because AF=AEDAF=DAE\angle DAF=\angle DAE
ADEF\therefore AD\bot EF
SADF=SADE\because S_{\triangle ADF}=S_{\triangle ADE}
SADF+SADE=2SADE=12ADFG+12ADEG=12ADEF\therefore S_{\triangle ADF}+S_{\triangle ADE}=2S_{\triangle ADE}=\frac{1}{2}AD\cdot FG+\frac{1}{2}AD\cdot EG=\frac{1}{2}AD\cdot EF
SADE=14ADEF\therefore S_{\triangle ADE}=\frac{1}{4}AD\cdot EF
故③正确;
AF=AE\because AF=AEFAE=90\angle FAE=90^{\circ}
EF2=AF2+AE2=2AE2\therefore EF^{2}=AF^{2}+AE^{2}=2AE^{2}
CE2+BE2=BF2+BE2=EF2\therefore CE^{2}+BE^{2}=BF^{2}+BE^{2}=EF^{2}
CE2+BE2=2AE2\therefore CE^{2}+BE^{2}=2AE^{2}
故④正确,
综上所述,①③④正确,
故答案为:①③④.

解析

在等腰RtABCRt\triangle ABC中,BAC=90\angle BAC=90^{\circ}
AB=AC\therefore AB=AC
ABC=C=45\therefore \angle ABC=\angle C=45^{\circ}
FBBC\because FB\bot BC
FBC=90\therefore \angle FBC=90^{\circ}
ABF=45\therefore \angle ABF=45^{\circ}
C=ABF\therefore \angle C=\angle ABF
FAAE\because FA\bot AE
FAE=90\therefore \angle FAE=90^{\circ}
CAE=BAF=90BAE\therefore \angle CAE=\angle BAF=90^{\circ}-\angle BAE
CAE\triangle CAEBAF\triangle BAF中,
{C=ABFAC=ABCAE=BAF\left\{\begin{array}{l}{∠C=∠ABF}\\{AC=AB}\\{∠CAE=∠BAF}\end{array}\right.
CAE\therefore \triangle CAEBAF(ASA)\triangle BAF\left(ASA\right)
CE=BF\therefore CE=BFAE=AFAE=AF
故①正确;
如图,连接DFDF

DAE=45\because \angle DAE=45^{\circ}BAC=90\angle BAC=90^{\circ}
DAF=BAD+BAF=BAD+CAE=45\therefore \angle DAF=\angle BAD+\angle BAF=\angle BAD+\angle CAE=45^{\circ}
DAF=DAE\therefore \angle DAF=\angle DAE
DAF\triangle DAFDAE\triangle DAE中,
{AF=AEDAF=DAEAD=AD\left\{\begin{array}{l}{AF=AE}\\{∠DAF=∠DAE}\\{AD=AD}\end{array}\right.
DAF\therefore \triangle DAFDAE(SAS)\triangle DAE\left(SAS\right)
DF=DE\therefore DF=DE
BD2+BF2=DF2\because BD^{2}+BF^{2}=DF^{2}
BD2+CE2=DE2\therefore BD^{2}+CE^{2}=DE^{2}
故②错误;
如图,设EFEFADAD于点GG
AF=AE\because AF=AEDAF=DAE\angle DAF=\angle DAE
ADEF\therefore AD\bot EF
SADF=SADE\because S_{\triangle ADF}=S_{\triangle ADE}
SADF+SADE=2SADE=12ADFG+12ADEG=12ADEF\therefore S_{\triangle ADF}+S_{\triangle ADE}=2S_{\triangle ADE}=\frac{1}{2}AD\cdot FG+\frac{1}{2}AD\cdot EG=\frac{1}{2}AD\cdot EF
SADE=14ADEF\therefore S_{\triangle ADE}=\frac{1}{4}AD\cdot EF
故③正确;
AF=AE\because AF=AEFAE=90\angle FAE=90^{\circ}
EF2=AF2+AE2=2AE2\therefore EF^{2}=AF^{2}+AE^{2}=2AE^{2}
CE2+BE2=BF2+BE2=EF2\therefore CE^{2}+BE^{2}=BF^{2}+BE^{2}=EF^{2}
CE2+BE2=2AE2\therefore CE^{2}+BE^{2}=2AE^{2}
故④正确,
综上所述,①③④正确,
故答案为:①③④.

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