In the cube abcd-a1b1c1d1, M is the midpoint of Aa1

In the cube abcd-a1b1c1d1, M is the midpoint of Aa1


Connecting AC and BD to o, connecting BM, DM, OM, OC ', a'c', OC, let the side length of cube be 2, BM = DM is obtained from △ ABM ≌ △ ADM, and ≌ ≌ o is the midpoint of BD, Mo ⊥ BD, OM = √ 3, OC '= √ 6, MC' = 3 from RT △ AOM, RT △ a'c'm, RT △ OCC ', respectively



In the cube abcd-a1b1c1d1, M is the midpoint of Aa1


It is proved that: take the midpoint n of BD, connect c1n, Mn, C1M. Obviously, BC1 = DC1, BM = DM. So c1n ⊥ BD, Mn ⊥ BD. so ∠ c1nm is the plane angle of dihedral angle m-bd-c1. If the edge length of cube is 2a, it is easy to calculate, C1M = 3A, C1b = √ 6a, MB = √ 3a