sina+sinb+sinc=0,cosa+cosb+cosc=0,求cos(B-C)的值?

2sinc-sinb=sina cos c的最小值 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? sinA+sinB+sinc=0 cosA+cosB+cosC=0 cos(B-C) 在△ABC中,求证：a(sinB-sinC)+b(sinC-sinA)+c(sinA-sinB)=0 sinA / cos(A/2) = sinB / cos(B/2) = sinC / cos(C/2)为什么等于sinA/2=sinB/2=sinC/2 已知cosA = cosθ×sinC,cosB = sinθ×sinc,求(sinA)^2+(sinB)^2+(sinC)^2的值 已知sinA+sinB+sinC=0,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=0,cosa+cosb+cosc=0,则cos(a-b)的值是? sinA+sinB+sinC=0,cosA+cosB+cosC=o,则cos(A-B)=______帮帮忙 在三角形ABC中求证：a（sinB-sinC）+b（sinC-sinA）+c（sinA-sinB）=0 sina+sinb+sinc=0 cosa+cosb+cosc=0求证cos*2a+cos*2b+cos*2c=3|2 在△ABC中,sinA+sinB+sinC=0,cosA+cosB+cosC=0,求证：cos²A+cos²B+cos²C=3/2 在△ABC中,sinA+sinB+sinC=0,cosA+cosB+cosC=0.求证：cos²A+cos²B+cos²c=3／2. 已知sinA+sinB=sinC,cosA+cosB=cosC,求cos(A-B)的值 已知sinA+sinB=sinC,cosA+cosB=cosC,求cos(A-B)的值 cos (A/2)=2sin[(C-B)/2],求证sinC-sinB=1/2sinA