已知sina+sinb+siny=0,cosa+cosb+cosy=0,求cos(b-y)的值

来源：学生作业帮助网 编辑：六六作业网 时间：2025/01/20 03:05:49
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)的值已知sina

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

已知sina+sinb+siny=0,cosa+cosb+cosy=0,求cos(b-y)的值
sina+sinb+siny=0
-sina=sinb+siny
两边平方：
(sina)^2=(sinb)^2+2sinbsiny+(siny)^2--------1
cosa+cosb+cosy=0
-cosa=cosb+cosy
两边平方：
(cosa)^2=(cosb)^2+2cosbcosy+(cosy)^2--------2
1+2:
2(sinbsiny+cosbcosy)=-1
2cos(b-y)=-1
cos(b-y)=-1/2

正确

sina=-(sinb+siny)
cosa=-(cosb+cosy)
然后根据(sina)^2+(cosa)^2=1
得到：
(sinb+siny)^2+(cosb+cosy)^2=1
化简得到:
2+2cosbcosy+2sinbsiny=1
即2cos(b-y)=-1
即cos(b-y)=-1/2

已知sina+sinb+siny=0,cosa+cosb+cosy=0,则cos（a-b)=? 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 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 三角恒等变换1已知sina+sinb+siny=0,cosa+cosb+cosy=0,求cos(b-y)的值 已知锐角a b y 且 sina+siny=sinb,cosa-cosy=cosb,求a-b的值 已知sina+sinB+siny=o,cosa+cosB+cosy=o,哪么cos(B-y)的值为多少 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 sina+sinb+siny=0.cosa+cosb-cosy=0,则cos(a-b)的值是, 在△ABC中,求证：a(sinB-sinC)+b(sinC-sinA)+c(sinA-sinB)=0 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 (sina/sinb)^2+(cosacosy)^2=1求证(tana/tanb)^2=(siny)^2 已知在△ABC中,sinA(sinB+sinB)-sinC=0,sinB+sin2C=0,求角A、B、C的大小