
(tan10°—√3)sin40°的值为
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(tan10°—√3)sin40°
=(tan10°-tan60°)sin40°
=(sin10°/cos10° - sin60°/cos60°) sin40°
=(sin10°cos60°-cos10°sin60°)sin40°/(cos10°cos60°)
=-sin50°sin40°/(cos10°cos60°)
=-2cos40°sin40°/(2cos10°cos60°)
=-sin80°/cos10°
=-1
=(tan10°-tan60°)sin40°
=(sin10°/cos10° - sin60°/cos60°) sin40°
=(sin10°cos60°-cos10°sin60°)sin40°/(cos10°cos60°)
=-sin50°sin40°/(cos10°cos60°)
=-2cos40°sin40°/(2cos10°cos60°)
=-sin80°/cos10°
=-1
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