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Cos20° Cos40° Cos80°

cos20°cos40°cos80° =2sin20°cos20°cos40°cos80°/(2sin20°) =sin40°cos40°cos80°/(2sin20°) =sin80°cos80°/(4sin20°) =sin160°/(8sin20°) =sin20°/(8sin20°) =1/8;

cos20°cos40°cos60°cos80° =(sin20cos20cos40cos60cos80)/sin20..........(乘以sin20°.再除以sin20°) =(sin40°cos40°cos60°cos80°)/2sin20°..........(2倍角公式) =(sin80°cos60°cos80°)/4sin20°................(2倍角公式) =(sin160°co...

不知道你是要求分开的值还是乘起来的值,如果是后者就简单了。 cos20°cos40°cos80° =2sin20°cos20°cos40°cos80°/2sin20° =sin40°cos40°cos80°/2sin20° =sin80°cos80°/4sin20° =sin160°/8sin20° =sin20°/8sin20° =1/8 谢谢望采纳

∵sinαcosα=1/2sin2α ∴sin20°cos20°=1/2sin40° sin40°cos40°=1/2sin80° sin80°cos80°=1/2sin160° ∴ =(sin40°cos40°cos60°cos80°)/2sin20° =(sin80°cos60°cos80°)/4sin20° =(sin160°cos60°)/8sin20° ∵sin(π-α)=sinα ∴sin160°=sin(180°-160°)...

cos20°-cos40°-cos80°=cos20°-cos(60°-20°)-cos(60°+20°)=cos20°-(cos60°cos20°+sin60°sin20°)-(cos60°cos20°-sin60°sin20°)=cos20°-cos60°cos20°-sin60°sin20°-cos60°cos20°+sin60°sin20°=cos20°-2cos60°cos20°=cos20°-cos20°=0.故答...

cos20°cos40°cos60°cos80° =(sin20cos20cos40cos60cos80)/sin20.(乘以sin20°.再除以sin20°) =(sin40°cos40°cos60°cos80°)/2sin20°.(2倍角公式) =(sin80°cos60°cos80°)/4sin20°.(2倍角公式) =(sin160°cos60°)/8sin20°.(2倍角公式) =sin(1...

cos20cos40cos80 =sin20cos20cos40cos80/sin20 =(1/8)sin160/sin20=(1/8)

cos40 + cos60 + cos80 + cos160 = cos(60-20)+ cos60 + cos(60+20)+cos(180-20) = cos60cos20 + sin60sin20 + cos60 + cos60cos20 -sin60sin20 + cos180cos20 + sin180sin20 = 1/2 cos20 + 1/2 + 1/2 cos20 -cos20 +0

cos160=—cos20然后 cos20°cos40°cos60°cos80° =(sin20cos20cos40cos60cos80)/sin20.(乘以sin20°.再除以sin20°) =(sin40°cos40°cos60°cos80°)/2sin20°.(2倍角公式) =(sin80°cos60°cos80°)/4sin20°.(2倍角公式) =(sin160°cos60°)/8sin20°.(...

cos20cos40cos80 =8sin20cos20cos40cos80/(8sin20) =4sin40cos40cos80/(8sin20) =2sin80cos80/(8sin20) =sin160/(8sin20) =sin20/(8sin20) =1/8

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