ok取BC中点设为H连接OH,HC1,A1C1,AC∵O,H分别为AB,BC中点∴OH||AC在正方体ABCD-A1B1C1中AC||A1C1∴OH||A1C1A1,O,H,C1共面连接BD交OH于E,连接B1D1交A1C1于F,连接EFB1D1⊥A1C1A1C1⊥BB1∴A1C1⊥面BDD1B1EF在面BDD1B1中...