已知sina+sinb+sinc=0且cosa+cosb+cosc=0 求cos(a-b)的值
已知sina+sinb+sinc=0且cosa+cosb+cosc=0 求cos(a-b)的值
已知sinA+sinB=sinC,cosA+cosB=cosC,求cos(A-B)的值
已知sinA+sinB+sinC=0,cosA+cosB+cosC=0,求cos(A-B)的值
sinA+sinB+sinC=0; cosA+cosB+cosC=0,求cos(B-C)的值?
sina+sinb+sinc=0,cosa+cosb+cosc=0,求cos(B-C)的值?
(1)已知sinA+sinB+sinC=0,cosA+cosB+cosC=0.求cos(B-C)的值.
已知sina+sinb+sinc=0,cosa+cosb+cosc=0,则cos(a-b)的值是?
sinA+sinB+sinC=0,cosA+cosB+cosC=o,则cos(A-B)=______
已知 A+B+C=π,sinA+sinB+sinC=cosA+cosB+cosC.求 ( cos2A+cos2B+cos
已知锐角abc满足sina+sinc=sinb,cosa-cosc=cosb,求a-b的值
sinA+sinB+sinc=0 cosA+cosB+cosC=0 cos(B-C)
cosa+cosb+cosc=sina+sinb+sinc=0 求(cosa)^2+(cosb)^2+(cosc)^2