已知sina+sinβ+siny=0,cosa+cosβ+cosy=0,求cos(β-y)的值?

已知sina+sinβ+siny=0,cosa+cosβ+cosy=0,求cos(β-y)的值? 已知sina-cosb+siny=0,cosa+cosb-cosy=0,求sin（a-b）的值 已知sinα +sinβ+ siny=0,cosα +cosβ +cosy=0,求cos(α-β) 三角函数不等式1)已知x+y+z=∏/2,x,y,z>0,求证:8(cosx·cosy·cosz)²≥27sinx·siny·sinz2)已知A+B+C=∏,A,B,C>0,试确定1/sin(A/2)+1/sin(B/2)+1/sin(C/2)与(1/sinA+1/sinB+1/sinC)(sinA+sinB+sinC)·2/3的大小关系,并证明.1)已知x 已知sina+sinb+siny=0,cosa+cosb+cosy=0,则cos（a-b)=? 已知:sina^2/sinβ^2 +cosa^2cosy^2=1 , 求证 tana^2/tanβ^2=siny^2a,β均为锐角,且cosacosβ-sinasinβ=sinacosβ-cosasinβ,则tana= ? 已知sina+sinb+siny=0,cosa+cosb+cosy=0.(1)求cos(a-b)的值;(2)若a.b.y属于【0,3分之4派】求sin(a+b+y)值 已知sinα+sinβ+siny=0,cosα+cosβ+cosy=0,求cos（β-y）的值 已知sina+sinb+siny=0,cosa+cosb+cosy=0,求cos(b-y)的值 .已知sina+sinb+siny=0,cosa+cosb+cosy=0,求cos（b-y）的值.（解题 已知锐角abc满足sina-sinb+siny=0,cosa-cosb-cosy=0,求a-b 已知COSa+COSb+COSy=0,SINa+SINb+SINy=0,求COS(b-y)的值 求函数z=sinx+siny+sin(x+y)(0 已知cosB = cos θ*sinA,cosC = sinθ*sinA.θ为已知角.则sin^2 A + sin^2 B +sin^2C等于多少? 已知x,y,z属于(0,派/2),sin^2x+sin^2y+sin^2z=1,求(sinx+siny+sinz)/(cosx+cosy+cosz)的最大值 已知sin A+sinB +siny=0 ,cos A+cos B+cosy=0,求cos(B -y)的值. 已知xy-sin(πy^2)=0 x^2y+siny^2=0求y的一阶导数 已知sina+sinb=siny,cosa+cosb=cosy,求证cos(a-y)=1/2