5.式子sin10°•sin30°•sin50°• - 知识问答

5.式子sin10°•sin30°•sin50°•sin70°的值为多少

1个回答

原式=cos80*1/2*cos40cos20
=(1/2)*2sin20cos20cos40cos80/(2sin20)
=sin40cos40cos80/(4sin20)
=2sin40cos40cos80/(8sin20)
=sin80cos80/(8sin20)
=2sin80cos80/(16sin20)
=sin160/(16sin20)
=sin20/(16sin20)
=1/16

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