如图12-32,已知ae交bc于点d,∠1=∠2=∠3,ab=ad
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∵四边形ABCD是平行四边形,∴AD=BC,AB=CD∴∠BAE=∠DEA.∵AE平分∠BAD,∴∠BAE=∠DAE.∴∠DEA=∠DAE.∴AD=DE.∵AD=DF∴DE=DF∵AB=5,∴CD=5
(1)、如图∵四边形ABCD是平行四边形∴AB∥=CD,BC∥=AD,∠BAD=∠C,∠ADC=∠B∵DF⊥BC∴DF⊥AD∴△ADG是直角三角形∵AM=MG∴AM=MG=DM=2∴∠ADM=∠DAM
如图,作EH⊥BC.则⊿ABP≌⊿PHE(AAS),PH=ABEH=BP-BC=PH-PC=CH.∠ECH=45°, ∠ECF=45°
证明:(1)∵四边形ABCD为平行四边形,∴AB∥DC,∴∠ABE=∠ECF,又∵E为BC的中点,∴BE=CE,在△ABE和△FCE中,∵∠ABE=∠ECFBE=CE∠AEB=∠FEC(对顶角相等),
∵△AGB∽△FGD∴AG:FG=BG:DG∵△AGD∽△EGB∴EG:AG=BG:DG∴EG:AG=AG:FG再问:额我们还没教相似,老师不允许用···再答:那就换一种:因为AB平行CD所以AG/G
证明:∵∠CDE=∠1+∠C,∠CDE=∠3+∠E∴∠1+∠C=∠3+∠E∵∠1=∠3∴∠C=∠E∵∠1=∠2,AB=AD∴△ABE≌△ADC(AAS)∴AC=AE
由AB=AC,DB=DC且AD=AD,故△ABD全等于△ADC,故角BAD=角DAC,又AB=AC,AE=AE,故△ABE全等于△ACE.故BE=EC,角AEB=角AEC=90°,即AE垂直BC.△A
∵AB=BC,BE=BD,∠ABE+∠CBD=120°∴△ABE≌△BCD∴∠BCD=∠BAE∵AB=BC,∠ABC=∠BGC=60°∴△ABF≌△CBG∴BF=BG
∵BE²=EF×EA∴BE/EF=EA/BE∵∠BEF=∠AEB∴△BEF∽△AEB∴∠EBF=∠EAB∵AD∥BC∴∠EBF=∠ADB∴∠EAB=∠ADB∵∠ABF=∠DBA∴△ABF∽△
(1)要判断BE与圆是否相切,只要证明AC是否与BE垂直即可,垂直即相切,不垂直就不相切.因为两个直角三角形ABE和ABC中BC/AB=9/12=3/4,AB/AE=12/16=3/4,所以两个三角形
证明:∵AE⊥EF∴∠AED+∠CEF=∠AED+∠DAE=90°∴∠DAE=∠CEF∵BE平分∠ABC∴∠EBC=∠CEB=45°∴BC=CE=AD∵∠C=∠D=90°∴△ADE≌△ECB∴AE=E
延长AE、BC交于点F,∵AD∥BC,∴∠DAE=∠CFE,∵AE平分∠BAD,∴∠DAE=∠BAF,∴∠BAF=∠CFE,∴AB=BF,∵AB=BC+AD,BF=BC+CF,∴AD=CF,∴△ADE
∵AB∥CD∴∠BAC=∠DCA(两直线平行,内错角相等)∵AE平分∠BACCF平分∠DCA∴∠ACF=1/2∠DCA∠CAE=1/2∠BAC∴∠ACF=∠CAE∴AE∥CF(内错角相等,两直线平行)
证明:在△ABE和△ACE中AE=AEAB=ACEB=EC∴△ABE≌△ACE(SSS),∴∠BAD=∠CAD,∵AB=AC,∴AD⊥BC.
(1)∵四边形ABCD是平行四边形,∴AD=BC,AB∥DC.∴∠BAE=∠DEA.∵AE平分∠BAD,∴∠BAE=∠DAE.∴∠DEA=∠DAE.∴AD=DE.∴DE=BC.(2)AB=DG+FC∵
证明:因为.AB=CD,BC=AD,所以.四边形ABCD是平行四边形,AD平行于BC,所以.角BAD=角BCD,角DAE=角AEB,因为.AE平分角BAC,CF平分角BCD,所以.角DAE=2分之1角