已知0已知0
已知0tan(a/2)+[1/tan(a/2)] =[sin(α/2)/cos(α/2)]+cos(α/2)/(sin(α/2) ={[sin(α/2)]^+[cos(α/2)]^}/sin(α/2)cos(α/2) =2/sinα=5/2 sinα=4/5 ∵0