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cos20cos40cos80=？希望有详细的过程.

2011-02-05 17:33:14a***
cos20cos40cos80=？希望有详细的过程.：cos20cos40cos80 =2sin20cos20cos40cos80/2sin20 =sin4?

最佳回答

  • cos20cos40cos80 =2sin20cos20cos40cos80/2sin20 =sin4cos40cos80/2sin20 =(1/2)sin80cos80/2sin20 =(1/4)sin160/2sin20 =(1/4)sin20/2sin20 =1/8
    2011-02-05 17:38:17
  • cos20cos40cos80 =(1/2sin20)*(2sin20cos20cos40cos80) =(1/2sin20)*(sin40cos40cos80) =1/4*(1/sin20)*(sin80cos80) =1/8*(1/sin20)*sin160 =1/8*(sin20/sin20) =1/8 注:以上省略了“度”.
    2011-02-05 17:43:08
    • 很赞哦！ (249)

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