In the cube abcd-a1b1c1d1, e is the midpoint of d1d, f is the midpoint of AB, and EC is at an angle with FB1

In the cube abcd-a1b1c1d1, e is the midpoint of d1d, f is the midpoint of AB, and EC is at an angle with FB1


Connect AC, BD, O, EO,
Then o is the midpoint of BD,
EO is the median line of triangle dbd1,
∴EO//BD1,
∵ EO ∈ plane EAC,
∴D
1B / / plane EAC



In the cube abcd-a1b1c1d1, the point E is the midpoint of d1d, and the EAC of D1b ‖ plane is proved


Connect AC, BD, O, EO,
Then o is the midpoint of BD,
EO is the median line of triangle dbd1,
∴EO//BD1,
∵ EO ∈ plane EAC,
{D1b / / plane EAC