—Very well.
A:What
B:Where
C:How
正方体ABCD﹣A1B1C1D1的棱长为l,点F、H分别为A1D、A1C的中点.
(Ⅰ)证明:A1B∥平面AFC;
(Ⅱ)证明:B1H⊥平面AFC.
已知sin(π3+α)=13,则cos(5π6+α)=( )