(sin10°+sin20°)/(cos10°+cos20°)化简求值
来源:学生作业帮 编辑:百度作业网作业帮 分类:数学作业 时间:2024/04/26 01:16:20
(sin10°+sin20°)/(cos10°+cos20°)化简求值
(sin10°+sin20°)/(cos10°+cos20°) (和差化积得到下式)
=2sin15°cos5°/(2cos15°cos5°)
=tan15°
=tan(45°-30°)
=(1- tan30°)/(1+ tan30°)
=(1- 根号3/3)/(1+ 根号3/3)
=(3-根号3)/(3+根号3)
=(3-根号3)²/[(3+根号3)(3-根号3)]
=(12-6根号3)/6
=2 - 根号3
再问: sin10°+sin20°)/(cos10°+cos20°) (和差化积得到下式) =2sin15°cos5°/(2cos15°cos5°) 能把这部分说详细点么?谢了
再答: sin10°+sin20°=sin(15°-5°)+sin(15°+5°) =(sin15°cos5° -cos15°sin5°) + (sin15°cos5° +cos15°sin5°) =2sin15°cos5° 而: cos10°+cos20°=cos(15°-5°)+cos(15°+5°) =(cos15°cos5° +sin15°sin5°) + (cos15°cos5° -sin15°sin5°) =2cos15°cos5° 所以:(sin10°+sin20°)/(cos10°+cos20°) =2sin15°cos5°/(2cos15°cos5°)
=2sin15°cos5°/(2cos15°cos5°)
=tan15°
=tan(45°-30°)
=(1- tan30°)/(1+ tan30°)
=(1- 根号3/3)/(1+ 根号3/3)
=(3-根号3)/(3+根号3)
=(3-根号3)²/[(3+根号3)(3-根号3)]
=(12-6根号3)/6
=2 - 根号3
再问: sin10°+sin20°)/(cos10°+cos20°) (和差化积得到下式) =2sin15°cos5°/(2cos15°cos5°) 能把这部分说详细点么?谢了
再答: sin10°+sin20°=sin(15°-5°)+sin(15°+5°) =(sin15°cos5° -cos15°sin5°) + (sin15°cos5° +cos15°sin5°) =2sin15°cos5° 而: cos10°+cos20°=cos(15°-5°)+cos(15°+5°) =(cos15°cos5° +sin15°sin5°) + (cos15°cos5° -sin15°sin5°) =2cos15°cos5° 所以:(sin10°+sin20°)/(cos10°+cos20°) =2sin15°cos5°/(2cos15°cos5°)
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