如图,三棱柱ABC-A1B1C1中,AA1⊥平面ABC,AB⊥BC,点M,N分别为A1C1与A1B的中点. (Ⅰ)求证:MN∥平面 BCC1B1; (Ⅱ)求证:平面A1BC⊥平面A1ABB1.
问题描述:
如图,三棱柱ABC-A1B1C1中,AA1⊥平面ABC,AB⊥BC,点M,N分别为A1C1与A1B的中点.
(Ⅰ)求证:MN∥平面 BCC1B1;
(Ⅱ)求证:平面A1BC⊥平面A1ABB1.
答
证明:(Ⅰ)连接BC1∵点M,N分别为A1C1 A1B的中点,∴MN∥BC1∵MN⊄平面BCC1B1,BC1⊂平面BCC1B1,∴MN∥平面BCC1B1.(Ⅱ)∵AA1⊥平面ABC,BC⊂平面ABC,∴AA1⊥BC.又∵AB⊥BC,AA1∩AB=A,∴BC⊥平面A1ABB1∵BC...