设AB=a(向量),AD=b,AA1=c.
则AC1=a+b+c.A1B=a-c.A1D=b-c
AC1·A1B=(a+b+c)·(a-c)=a²-c²=0,∴AC1⊥A1B
AC1·A1D=(a+b+c)·(b-c)=b²-c²=0 ∴AC1⊥A1D.
∴AC1⊥平面A1BD.
设AB=a(向量),AD=b,AA1=c.
则AC1=a+b+c.A1B=a-c.A1D=b-c
AC1·A1B=(a+b+c)·(a-c)=a²-c²=0,∴AC1⊥A1B
AC1·A1D=(a+b+c)·(b-c)=b²-c²=0 ∴AC1⊥A1D.
∴AC1⊥平面A1BD.