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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 诱导公式口诀“奇变偶不变,符号看象限”意义: k×π/2±a(k∈z)的三角函数值。 (1)当...

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...

∵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°)...

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

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

本题也可用三倍角公式解:cos3x=4cosxcos(60°-x)cos(60°+x) cos20°cos40°cos60°cos80°=(1/2)cos20°cos40°cos80° =(1/2)cos20°cos(60°-20°)cos(60°+20°) =(1/2)(1/4)cos(3*20°) =(1/2)(1/4)(1/2)=1/16

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

利用计算器可算出:cos20°≈0.9397,cos40°≈0.7660,cos60°=0.5,cos80°≈0.1736,∴cos20°>cos40°>cos60°>cos80°∴在锐角范围内,余弦函数值随着角度的增大而减小,即余弦值,角大值小.故答案是0.9397,0.7660,0.5,0.1736,小.

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...

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...

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