正弦余弦的问题
sin10度cos20度cos40度等于多少
sin10°cos20°cos40° =sin(90°-10°)cos20°cos40° =coa80°cos20°cos40° =1/(8sin20°)*8sin20°cos20°cos40°cos80° =1/(8sin20°)*4sin40°cos40°cos80° =1/(8sin20°)*2sin80°cos80° =sin160°/(8sin20°) =sin(180°-20°)/(8sin20°) =sin20°/(8sin20°) =1/8.
sin10cos20cos40 =coa80cos20cos40 =1/(8sin20)*8sin20cos20cos40cos80 =1/(8sin20)*4sin40cos40cos80 =1/(8sin20)*2sin80cos80 =sin160/(8sin20) =sin20/(8sin20) =1/8.
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