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.