（1）如图,在三角形ABC中,∠BAC=90°,AB=AC,点D在BC上,且BD=BA,点E在BC的延长线上,且CE=CA,

由题意知:∠BAD=∠BDA,∠BDA=∠DCA+∠DAC,∠CEA=∠EAC,
∠DCA=∠CEA+∠EAC=2∠EAC.
设,∠BAD=X,∠DAC=Y,∠EAC=Z
∠BAC=X+Y,∠DAE=Y+Z
,∠BDA=,∠BAD=Y+∠DCA=Y+∠EAC+∠CEA=Y+2Z
即X=Y+2Z
所以∠BAC=X+Y=Y+2Z+Y=2(Z+Y)
∠DAE=Z+Y
所以∠BAC=X+Y=Y+2Z+Y=2(Z+Y)=2∠DAE