(2) If the midpoint g of A 1D 1 is taken, then the FG⊥ plane a 1b 1d 1 and EF is at the bottom A1b/kloc.
In Rt△GEF, Tan ∠ GEF = 22, so the angle formed by EF and bottom A1b1c1d1is Arctan 22. (12).