证明sinA+sin(A+2π/3)+sin(A-2π/3)=0

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证明sinA+sin(A+2π/3)+sin(A-2π/3)=0
证明sinA+sin(A+2π/3)+sin(A-2π/3)=0

证明sinA+sin(A+2π/3)+sin(A-2π/3)=0
证明sinA sin(A 2π/3) sin(A-2π/3)=0
nA sin（A 2/3π） cos（A 5/6π）
=sina sinacos2/3pai sin2/3paicosa cosacos5/6pai-sinasin5/6pai
=sina-1/2sina 根号3/2cosa-根号3/2cosa-1/2sina
=0


sinA+sin(A+2π/3)+sin(A-2π/3)
=sinA+sinAcos2π/3+cosAsin2π/3+sinAcos2π/3-cosAsin2π/3
=sinA+2sinAcos2π/3
=sinA+2sinA*(-1/2)
=sinA-sinA
=0.

d

(b-3)/(sin45-sin15)=4/sin45 因：sin45-sin15= 2cos30sin15 √2/2-sin15=√3sin15 sin15=(√6-√2)/4 所以：b=a/sinA*sinB =12√2/[

证明sinA+sin(A+2π/3)+sin(A-2π/3)=0 证明sinA+sin(A+2π/3)+sin(A-2π/3)=0 证明(sinA)^2+[sin(A+2π/3)]^2+[sin(A-2π/3)]^2=3/2 证明根号3sina-cosa=2sin(a-π/6) 证明：[sin(a-60)]^2+[sina]^2+[sin(a+60)]^2=3/2 sina(cosa)^3=1/4sin 2a+1/8sin 4a证明过程 证明sin^2a+sin^2β+1>sina*cosa+sina+sinβ 1- sin(2π/3 - a)/sina 怎么证明2sinA*cosA=sin(2A) tan(A+B)=2tanB 证明3sinA=sin(A+2B) tan(A+B)=2tanB 证明3sinA=sin(A+2B)笑嘻嘻 sinb/sina=cos(a+b),证明3sinb=sin(2a+b) 1.利用公式C(a-b)、S(a-b)证明：（1）cos(3排除以2-a)=-sina (2)sin(3排除以2-a)=-cosa (3)cos(排-a...1.利用公式C(a-b)、S(a-b)证明：（1）cos(3排除以2-a)=-sina (2)sin(3排除以2-a)=-cosa (3)cos(排-a)=-cosa (4)sin(排-a)=sina 证明sin(2a+b)/sina-2cos(a+b)=sinb/sina 证明sin(2a+b)/sina-2cos(a+b)=sinb/sina 证明sina sin(a+2b) - sinb sin(b+2a) =sin(a+b)sin(a-b) sinA=3sin(2π/3-A) SINA=?sinA=3sin(2π/3-A) SINA=?答案是-3√3cosA sinA+sin(90°-A)+1/sinA-sin(90°-A)+1=cot(A/2) 请问这怎么证明,