12. 如图在棱长为2的正方体ABCD−A1B1C1D1ABCD-A_{1}B_{1}C_{1}D_{1}ABCD−A1B1C1D1中,点EEE是ADADAD的中点,那么异面直线D1ED_{1}ED1E和A1BA_{1}BA1B所成的角的余弦值等于((( )))