cos36-cos72
cos36一cos72 -
解：cos36°-cos72° =sin54°-sin18° =sin（36°+18°）sin（36°-18°）sin36°cos18°+cos36°sin18°-sin36°cos18°+cos36°sin18° =2cos36°sin18° =2cos36°sin18°cos18°/cos18° =cos36°sin36°/cos18° =sin72°/2cos18° =cos18°/2cos18° =1/2 后面会介绍。
=cos36°-cos（36*2）cos36°-（cos36°）2+(sin36)^2
解：cos36°-cos72° =sin54°-sin18° =sin（36°+18°）sin（36°-18°）sin36°cos18°+cos36°sin18°-sin36°cos18°+cos36°sin18° =2cos36°sin18° =2cos36°sin18°cos18°/cos18° =cos36°sin36°/cos18° =sin72°/2cos18° =cos18°/2cos18° =1/2 后面会介绍。
=cos36°-cos（36*2）cos36°-（cos36°）2+(sin36)^2
Cos36-cos72 =(sin36cos36-sin36cos72)/sin36 =-(sin108-sin36-sin72)/2sin36 =-(sin72-sin36-sin72)/2sin36 =sin36/2sin36 =1/2 积化和差公式：sinα·cosβ=(1/2)[sin(α+β)+sin(α-β)]cosα·sinβ=(1/2)[sin(α+β)-sin(α-β)]cosα·cosβ=(1/2)[cos(到此结束了？。
cosθ-cosφ=-2sin[(θ+φ)/2]sin[(θ-φ)/2]
cos72度减cos36度怎么算 -
Cos36-cos72 =(sin36cos36-sin36cos72)/sin36 =-(sin108-sin36-sin72)/2sin36 =-(sin72-sin36-sin72)/2sin36 =sin36/2sin36 =1/2cos72度减cos36度=-0.5
1）先解出sin18,设sin18=x.因为cos36=sin54,注意36=18*2,54=18*3,由2 倍角和3倍角公式，得1-2x^2=3x-4x^3,即4x^3-2x^2-3x+1=（x-1)(4x^2+2x-1)=0,由于sin18≠1,解4x^2+2x-1=0得x=（√5-1）4=sin18 2)x=cos36-cos72=1-2(sin18)^2-sin18=0.5 另解co说完了。
cos36-cos72如何化简求值 -
cos36-cos72 =cos(54-18)-cos(54+18)=cos54cos18+sin54sin18-[cos54cos18-sin54sin18]=2sin54sin18 =-2sin54sin(-18)=2sin54sin18 =2cos36sin18 =2cos36sin18cos18/cos18 =cos36sin36/cos18 =sin72/(2cos18)=sin72/(2sin72)=1/2 参考资料：等我继续说。
按传统的方法做，计算量很大。可以用图形结合如图：做∠A=36°，∠ABC=∠C=72° ∠DBC=36°，∠BDC=∠C=72° 设AD=BD=1,设AE=EB=a，DF=CF=c COS36°=AE/AD=a COS72°=DF/BD=c COS36°-COS72°=a-c 又因为AB=AC,即2a=1+2c a-c=1/2 所以COS36°-COS72°=1/2 到此结束了？。
cos72-cos36的计算过程 -
cos36-cos72 =cos(54-18)-cos(54+18)=cos54cos18+sin54sin18 - [cos54cos18-sin54sin18]=2sin54sin18 =2sin(90-36)sin18 =2cos36sin18 =2cos36sin18 cos18/cos18 =cos36sin36/cos18 =sin72/(2cos18)=sin72/(2cos(90-72))=sin72/(2sin72)=1/2 是什么。
=sin36/2sin36 =1/2 解2. cos36-cos72 =cos(54-18)-cos(54+18)=cos54cos18+sin54sin18-[cos54cos18-sin54sin18]=2sin54sin18 =2cos36sin18 =2cos36sin18cos18/cos18 =cos36sin36/cos18 =sin72/(2cos18)=sin72/(2sin72)=1/2 解3. 做单位向量OA=(cos0,sin0),OB=(是什么。