会不会是(cos²10°-1)*(1-√3tan10°)
cos²10°-1)*(1-√3tan10°)
=[(1+cos20°)/2-1]*(1-√3tan10°)
=[(cos20°-1)/2]*[(cos10°-√3sin10°)/cos10°]
=[(cos20°-1)/2]*[2sin20°/cos10°]
=2(cos20°-1)sin10°
=2cos20°sin10°-2sin10°
=1/2-3sin10°