半径为R的圆外接与三角形ABC 且2R(sin^2A-sin^2c)=(根号3*a-b)sinB求角C

2R(sinA+sinC)(sinA-sinC)=(√3a-b)sinB
有正弦定理
2RsinA=a,2RsinC=c
所以(a+c)(sinA-sinC)=(√3a-b)sinB
sinA=a/2R,sinB=b/2R,sinC=c/2R
所以(a+c)(a-c)=(√3a-b)b
a^2-c^2=√3ab-b^2
a^2+b^2-c^2=√3ab
cosC=(a^2+b^2-c^2)/2ab=√3/2
C=30度