作业帮如何证明cos a +cos b =2*(cos(a+b)/2)*(cos(a-b)/2) 速度
来源：学生作业帮助网 编辑：作业帮 时间：2024/11/03 00:37:25
如何证明cos a +cos b =2*(cos(a+b)/2)*(cos(a-b)/2) 速度
如何证明cos a +cos b =2*(cos(a+b)/2)*(cos(a-b)/2) 速度
如何证明cos a +cos b =2*(cos(a+b)/2)*(cos(a-b)/2) 速度
可以从右往左证明：
右边 = 2*(cos(a+b)/2)*(cos(a-b)/2)
= 2 * cos(a/2+b/2) * (cos(a/2-b/2)
= 2 * { cosa/2 cosb/2 - sina/2 sinb/2 ) * { cosa/2 cosb/2 + sina/2 sinb/2 )
= 2 * { (cosa/2)^2 (cosb/2)^2 - [(1-(cosa/2)^2][1- (cosb/2 ) ^2 }
= 2 * { (cosa/2)^2 (cosb/2)^2 - [1 -(cosa/2)^2- (cosb/2 ) ^2+(cosa/2)^2 (cosb/2)^2 ] }
= 2 * { (cosa/2)^2 (cosb/2)^2 - 1 + (cosa/2)^2+ (cosb/2 ) ^2 - (cosa/2)^2 (cosb/2)^2 }
= 2 * { - 1 + (cosa/2)^2 + (cosb/2 ) ^2 }
= -2 + 2 (cosa/2)^2 + 2 (cosb/2 ) ^2
= 2 (cosa/2)^2 -1 + 2 (cosb/2 ) ^2 - 1
= cos a +cos b = 左边,得证.
如何证明cos a +cos b =2*(cos(a+b)/2)*(cos(a-b)/2) 速度
cosacosb=1/2[cos(a+b)+cos(a-b)]如何证明
如何证明|cos a-cos b | ≤| a - b
(cos a)^2 + (cos b)^2 =1证明
如何证明2cosA*cos(kA)-cos[(k-1)A]=cos[(k+1)A]
如何证明sin(a+b)=sin(a)cos(b)+cos(α)sin(b)
如何证明cos(A+B)=cosAcosB-sinAsinB
证明cos(A+B)
证明：cos(a+b)*cos(a-b)=cos2b-cos2a
如何证明在三角形中sinA+sinB+sinC=4coc(A/2)*cos(B/2)*cos(C/2)
如何证明sinA+sinB=2sin((A+B)/2)cos((A-B)/2)
证明sin(A+B)sin(A-B)=cos^2B-cos^2A
COS(4a)+4COS(2a)=[8(COSa)^4]-3求教如何证明
(sinA+sinB)/(cos A +cos B) =tan (A+B)/2 怎么证明?
证明sina*sinb=[cos(a-b)-cos(a+b)]/2
用cos (A-B)=cosAcosB+sinAsinB 证明（推导） cos^2(a/2)= (1+cos a) / 2
2cos(A/2)-1-cosA/2cos(A/2)+1+cosA=1-cos(A/2)/1+cos(A/2) 请问如何证明,
证明cos(A+B)=cosAcosB-sinAsinB