已知三棱柱ABC-A1B1C1中,侧棱垂直于底面,AC=BC,点D是AB的中点.(Ⅰ)求证:BC1∥平面CA1D;(Ⅱ)若

2025-04-26 20:14:57
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回答1:

解答:(Ⅰ)证明:连接AC1交A1C于点E,连接DE
因为四边形AA1C1C是矩形,则E为AC1的中点
又D是AB的中点,DE∥BC1
又DE?面CA1D,BC1?面CA1D,
所以BC1∥面CA1D;
(2)解:AC=BC,D是AB的中点,AB⊥CD,
又AA1⊥面ABC,CD?面ABC,AA1⊥CD,
AA1∩AB=A,CD⊥面AA1B1B,CD?面CA1D,
平面CA1D⊥平面AA1B1B所以CD是三棱锥B1-A1DC的高,
SA1B1D=

1
2
AB×
3
3

所以VB1?A1DCVC?A1B1D=
1
3
SA1B1D×AD=
1
3
×
3
×
3
=1;