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#c172177c-360e-4072-b489-b5de75ebf138中等解答题空间中的垂直立体几何

28.如图,在直三棱柱ABCA1B1C1ABC-A_{1}B_{1}C_{1}中,平面A1BCA_{1}BC\bot平面ABB1A1ABB_{1}A_{1},侧面$ABB_{1}A_{1

8.如图,在直三棱柱ABCA1B1C1ABC-A_{1}B_{1}C_{1}中,ACBCAC\bot BCAC=CC1=2BCAC=CC_{1}=2BC,则直线BC1BC_{1}与直线AB1AB_{1}夹角的余弦值为((  ))