Question

求这题的过程和答案，谢谢

Answer 1

原式=tan70cos10(tan60tan20-1)
=tan70cos10(sin60sin20-cos60cos20)/(cos60cos20)
=-tan70cos10cos(60+20)/cos60cos20
=-cot20cos10sin10/cos60cos20
=-cot20sin20/2cos60cos20
=-(cos20/sin20)sin20/2cos60cos20
=-1/4

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这题好像错了，正确答案好像是-1

追答

额
中间抄错了

tan70×cos10×(√3tan20-1)
=tan70×cos10×(tan60×tan20-1)
=tan70×cos10×[(sin60×sin20/cos60×cos20)-1]
=tan70×cos10×(sin60×sin20-cos60×cos20)/(cos60×cos20)
=tan70×cos10×[-cos(60+20)]/(cos60 ×cos20)
=-tan70×cos10×cos80/(cos60×cos20)
=-tan70×cos10×sin10/(cos60×cos20)
=-(sin70/cos70)×(1/2)×sin20/(cos60×cos20)
=-(cos20/sin20)×sin20/(2cos60×cos20)
=-1/(2cos60)
=-1

追问

http://zhidao.baidu.com/question/1894812171287623540.html?fr=index_nav&ssid=b5a5837713a2605dbe9908a9bcbbd16a.3.1403190158.1.kAhZHdhIzMxX&uid=1403190148388_108&tj=h5_mobile_1_0_10_title&step=2

http://zhidao.baidu.com/question/2052834994887814947.html?fr=index_nav&ssid=b5a5837713a2605dbe9908a9bcbbd16a.3.1403190158.1.kAhZHdhIzMxX&uid=1403190148388_108&tj=h5_mobile_1_0_10_title&step=2

http://zhidao.baidu.com/question/647606641437354285.html?fr=index_nav&ssid=b5a5837713a2605dbe9908a9bcbbd16a.3.1403190158.1.kAhZHdhIzMxX&uid=1403190148388_108&tj=h5_mobile_1_0_10_title&step=2

http://zhidao.baidu.com/question/873095976937275972.html?fr=index_nav&ssid=b5a5837713a2605dbe9908a9bcbbd16a.3.1403190158.1.kAhZHdhIzMxX&uid=1403190148388_108&tj=h5_mobile_1_0_10_title&step=2

Answer 2

解：tan70×cos10×(√3tan20-1) =tan70×cos10×(tan60×tan20-1) =tan70×cos10×[(sin60×sin20/cos60×cos20)-1] =tan70×cos10×(sin60×sin20-cos60×cos20)/(cos60×cos20) =tan70×cos10×[-cos(60+20)]/(cos60 ×cos20) =-tan70×cos10×cos80/(cos60×cos20) =-tan70×cos10×sin10/(cos60×cos20) =-(sin70/cos70)×(1/2)×sin20/(cos60×cos20) =-(cos20/sin20)×sin20/(2cos60×cos20) =-1/(2cos60) =-1

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对不起了，我已经采纳别的了。。。。。