若sina+sinb+siny=cosa+cosb+cosy=0,则cos(a-b)等于

若sina+sinb+siny=cosa+cosb+cosy=0,则cos(a-b)等于 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. sinA/sinB=cosB/cosA 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 已知锐角a b y 且 sina+siny=sinb,cosa-cosy=cosb,求a-b的值 sina+sinb+siny=0.cosa+cosb-cosy=0,则cos(a-b)的值是, 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 sina cosa=sinb cosb是什么三角形 sinA+sinB=sinC(cosA+cosB),化简, 三角恒等变换1已知sina+sinb+siny=0,cosa+cosb+cosy=0,求cos(b-y)的值 若sinA+2sinC=cosB,且cosA-2cosC=sinB,求证：sinAcosB+cosA