26.如图,在三棱锥A−BCDA-BCDA−BCD中,AB=AC=BD=CD=4AB=AC=BD=CD=4AB=AC=BD=CD=4,AD=BC=2AD=BC=2AD=BC=2,点MMM,NNN分别是ADADAD,BCBCBC的中点.(1)求AN→⋅CM→\overrightarrow{AN}\cdot \overrightarrow{CM}AN⋅CM的值;(2)求异面直线ANANAN,CMCMCM所成角的余弦值.