cos40°(1+√3tan10°)
=cos40°(1+√3sin10°/cos10°)
=cos40°(cos10°+√3sin10°)/cos10°
=2cos40°(cos10°/2+√3sin10°/2)/cos10°
=2cos40°(sin30°cos10°+cos30°sin10°)/cos10°
=2cos40°sin40°/cos10°
=sin80°/cos10°
=1