连结AB,AB1,在正方体AC1中,底面ABCD是正方形,∴ BD⊥AC；侧棱CC1⊥底面ABCD,∴BD⊥CC1,又CC1∩AC=C,由线面垂直的判定定理可知,BD⊥平面ACC1,∵AC1在平面ACC1内,∴BD⊥AC1；同理,A1B⊥AC1,∵BD∩A1B=B,∴AC1⊥平...