(1)证明:在直三棱柱ABC-A1B1C1中,D是AB中点,CD⊥AB,又BB1⊥CD,∴CD⊥平面ABB1A1 .
又∵A1B⊂平面ABB1A1,∴A1B⊥CD,又∵ABB1A1是正方形,AB1∥DE,A1B⊥DE.
CD∩DE=D,A1B⊥平面CDE.
(2)CD=
2,DE=
1
2AB1=2,∴S△CDE=
2
2
2=
2,A1M=A1B-BM=4-1-3,
∴VA1−CDE=
1
3×S△CDE×A1M=
2.
(1)证明:在直三棱柱ABC-A1B1C1中,D是AB中点,CD⊥AB,又BB1⊥CD,∴CD⊥平面ABB1A1 .
又∵A1B⊂平面ABB1A1,∴A1B⊥CD,又∵ABB1A1是正方形,AB1∥DE,A1B⊥DE.
CD∩DE=D,A1B⊥平面CDE.
(2)CD=
2,DE=
1
2AB1=2,∴S△CDE=
2
2
2=
2,A1M=A1B-BM=4-1-3,
∴VA1−CDE=
1
3×S△CDE×A1M=
2.