Question

4cos50º－tan40º求值

Answer 1

4cos50º-tan40º
=4sin40º-sin40º/cos40º
=(4sin40°cos40°-sin40°)/cos40°
=(2sin80°-sin40°)/cos40°
=[2cos10°-sin(30°+10°)]/cos40°
=(2cos10°-1/2cos10°-√3/2sin10°)/cos40°
=(3/2cos10°-√3/2sin10°)/cos40°
=√3(√3/2cos10°-1/2sin10°)/cos40°
=√3（cos30°cos10°-sin30°sin10°)/cos40°
=√3cos40°/cos40°
=√3

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Answer 2

追答

行家正解

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Answer 3

Answer 4

=(4sin40°cos40°-sin40°)/cos40° =(2sin80°-sin40°)/cos40° =[2cos10°-sin(30°+10°)]/cos40° =(2cos10°-1/2cos... /cos40° =(3/2cos10°-√3/2sin10°)/cos40° =√3(-√3/2cos10°-1/2sin10°)/cos40° =√3cos40°/cos40° =√3 可能...