sina+sinb+siny=0.cosa+cosb-cosy=0,则cos(a-b)的值是,

sina+sinb+siny=0.cosa+cosb-cosy=0,则cos(a-b)的值是, 已知sina+sinb+siny=0,cosa+cosb+cosy=0,则cos（a-b)=? 已知sina+sinb=siny,cosa+cosb=cosy,求证cos(a-y)=1/2 sinA+sinB+sinY=0 ,cosA+cosB+cosY=0,求cos(B-Y)的值. 若sina+sinb+siny=cosa+cosb+cosy=0,则cos(a-b)等于 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sina+sinB+siny=o,cosa+cosB+cosy=o,哪么cos(B-y)的值为多少 已知COSa+COSb+COSy=0,SINa+SINb+SINy=0,求COS(b-y)的值 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sina=sinb=siny=0,cosa=cosb=cosy=0,求cos(b-y)的值 三角恒等变换1已知sina+sinb+siny=0,cosa+cosb+cosy=0,求cos(b-y)的值 (sina/sinb)^2+(cosacosy)^2=1求证(tana/tanb)^2=(siny)^2 已知sin A+sinB +siny=0 ,cos A+cos B+cosy=0,求cos(B -y)的值. 已知SinA×sinB=1 求cos(A+B)=? sinA*sinB=1,则cos（A+B)=? sina*sinb=1则cos(a-b)= sinA*sinB=1,则cos(A+B)=?