Then, OG,BE and AD,CF will be four diagonals. DR's of OG=(a,a,a)=(1,1,1) DR's of BE=(−a,−a,a)=(1,1,−1) DR's of AD=(−a,a,a)=(−1,1,1) DR's of CF=(a,−a,a)=(1,−1,1) Let DR's of line be l,m and n. Therefore, angle between line and diagonal ‌‌‌‌‌cos‌α=‌