(1-tan21度)/(1+tan21度)等于tan24度是怎样算出来的..
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(1-tan21度)/(1+tan21度)等于tan24度是怎样算出来的..
我想了好久啊.
我想了好久啊.
(1-tan21度)/(1+tan21度)
=(cos21°-sin21°)/(cos21°+sin21°)
=√2(√2/2cos21°-√2/2sin21°)/[√2(√2/2cos21°+√2/2sin21°)
=√2/(sin45°cos21°-cos45°sin21°)/[√2/(cos45°cos21°+sin45°sin21°)]
=sin(45°-21°)/cos(45°-21°)
=sin24°/cos24°
=tan24°
再问: 为什么(1-tan21度)/(1+tan21度) =(cos21°-sin21°)/(cos21°+sin21°)?是不是有什么公式啊
再答: (1-tan21度)/(1+tan21度) =(1-sin21°/cos21°)/(1-sin21°/cos21°) =【(cos21°-sin21°)/cos21°】/【(cos21°+sin21°)/cos21°】 =(cos21°-sin21°)/(cos21°+sin21°)
=(cos21°-sin21°)/(cos21°+sin21°)
=√2(√2/2cos21°-√2/2sin21°)/[√2(√2/2cos21°+√2/2sin21°)
=√2/(sin45°cos21°-cos45°sin21°)/[√2/(cos45°cos21°+sin45°sin21°)]
=sin(45°-21°)/cos(45°-21°)
=sin24°/cos24°
=tan24°
再问: 为什么(1-tan21度)/(1+tan21度) =(cos21°-sin21°)/(cos21°+sin21°)?是不是有什么公式啊
再答: (1-tan21度)/(1+tan21度) =(1-sin21°/cos21°)/(1-sin21°/cos21°) =【(cos21°-sin21°)/cos21°】/【(cos21°+sin21°)/cos21°】 =(cos21°-sin21°)/(cos21°+sin21°)
化简:tan21度(1+tan24度)+tan24度
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