求sin10°x sin50°x sin70°的值

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求sin10°x sin50°x sin70°的值
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求sin10°x sin50°x sin70°的值
求sin10°x sin50°x sin70°的值

求sin10°x sin50°x sin70°的值
=sin10*cos(90-50)*cos(90-70)
=sin10cos20cos40
=2sin10cos10cos20cos40/2cos10
=sin20cos20cos40/2cos10
=2sin20cos20cos40/4cos10
=sin40cos40/4cos10
=2sin40cos40/8sin(90-10)
=sin80/8sin80
=1/8