sina-2sinB=0,cosa+2cosB=2,(1)求cosa,cos（a+B）（2）求2a+B

sina+sinb=0,cosa+cosb=2/3,cos2a+cos2b=?sina=-sinb即a=-b，为什么 求证:sina^2+sinb^2-sina^2*sinb^2+cosa^2*cosb^2=1 (1+sina-cosa)/sina * (1+sinb-cosb) /sinb=2,求tana*tanba,b是锐角. A,B,C∈(0,π/2),且SinA-SinC=SinB,CosA+CosC=CoSB,则B-A等于? 2SinA+CosB=2,SinB+2CosA=根号3,求角C 4sinA+2cosB=1 2sinB+4cosA=3根号3 求C 求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2 SinA=2SinB TanA=3TanB CosA=? sina+2sinb,tana=3tanb,则cosa= 已知sina=2sinb.tana=3tanb,cosa sina+cosa=1/2,sinb-cosb=1/3 判断三角形形状：（SINA+SINB)(COSA+COSB)=2SINC 求证：sina+sinb/(cosa+cosb)=tan[(a+b)/2] 已知sinA+cosA=2sina,sinA*cosA=(sinb)^2,求证4(cos2a)^2=(cos2b)^2 已知sinA+cosA=2sina,sinA*cosA=(sinb)^2,求证4(sin2a)^2=(cos2b)^2 sinA/sinB=cosB/cosA 3sina=2cosa 则(cosa-sina/cosa+sina)+(cosa+sina/cosa-sina)=______ 3sina=2cosa 则(cosa-sina/cosa+sina)+(cosa+sina/cosa-sina)=______