2+cos20°-sin的平方2 10°
=2+(1-2sin²20°)-sin²10°
=3-2sin²10°-sin²10°
=3-3sin²10°
=3cos²10°
∴ 根号2+cos20°-sin的平方2 10°
=√(3cos²10°)
=√3|cos10°|
=√3cos10°