如图,在△ABC中,AB=AC,BD=BC,AD=DE=EB,则∠A是( ) A.30° B.45° C.60° D.20°
问题描述:
如图,在△ABC中,AB=AC,BD=BC,AD=DE=EB,则∠A是( )
A. 30°
B. 45°
C. 60°
D. 20°
答
设∠A=x,
∵AD=DE,
∴∠DEA=∠A=x,
∵DE=EB,
∴∠EBD=∠EDB=
,x 2
∵∠BDC=∠A+∠DBA=x+
=x 2
,3x 2
∵AB=AC,BD=BC,
∴∠C=∠BDC=∠ABC=
,3x 2
∵∠A+∠ABC+∠C=180°,
即:x+
+3x 2
=180°,3x 2
∴x=45°,
∴∠A=45°.
故选B.