求值,(1)(sin7+cos15sin8)/(cos7 -sin15sin8)(2)cos40[1+(√3)tan10
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求值,(1)(sin7+cos15sin8)/(cos7 -sin15sin8)(2)cos40[1+(√3)tan10] 有过程
急需,快
急需,快
![求值,(1)(sin7+cos15sin8)/(cos7 -sin15sin8)(2)cos40[1+(√3)tan10](/uploads/image/z/18372598-70-8.jpg?t=%E6%B1%82%E5%80%BC%2C%281%29%28sin7%2Bcos15sin8%29%2F%28cos7+-sin15sin8%29%EF%BC%882%EF%BC%89cos40%5B1%2B%28%E2%88%9A3%29tan10)
答:
1)
(sin7+cos15sin8)/(cos7-sin15sin8)
=[sin(15-8)+cos15sin8] / [cos(15-8)-sin15sinb ]
=( sin15cos8 -cos15sin8+cos15sin8 ) / (cos15cos8+sin15sin8 -sin15sin8)
=sin15cos8 / (cos15cos8)
=tan15
=2sin15cos15/2cos²15
=sin30/(1+cos30)
=2-√3
2)
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
1)
(sin7+cos15sin8)/(cos7-sin15sin8)
=[sin(15-8)+cos15sin8] / [cos(15-8)-sin15sinb ]
=( sin15cos8 -cos15sin8+cos15sin8 ) / (cos15cos8+sin15sin8 -sin15sin8)
=sin15cos8 / (cos15cos8)
=tan15
=2sin15cos15/2cos²15
=sin30/(1+cos30)
=2-√3
2)
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
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