如图,在直三棱柱ABC--A1B1C1中,AC⊥BC,点D是AB的中点

2025-04-03 19:00:21
推荐回答(1个)
回答1:

证明:(1)在直三棱柱ABC--A1B1C1中,有:BB1⊥平面ABC
又AC在平面ABC,那么:BB1⊥AC
而已知:AC⊥BC,这就是说直线AC垂直于平面BCC1B1内的两条相交直线BB1.BC
所以由线面垂直的判定定理可得:
AC⊥平面BCC1B1
又BC1在平面BCC1B1内,所以:AC⊥BC1
(2)设侧面矩形BCC1B1对角线BC1与B1C交于点O,连结OD
则易知点O是对角线BC1的中点
又点D是AB的中点,那么在△ABC1中:
中位线OD//AC1
又OD在平面B1CD内,AC1不在平面B1CD内
所以由线面平行的判定定理可得:
AC1∥平面B1CD

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