sin(α+7π/6)=sin(α-π/6+4π/3)=sin(α-π/6)cos(4π/3)+cos(α-π/6)sin(4π/3)求出sin(α-π/6)=(1-cos(α-π/6)^2)^(1/2)=?（题目中的那个余弦值弄不明白怎么写的）cos(4π/3)=-1/2,sin(4π/3)=-√3/2,代入最...