△ABC,所蚂答消以sinC=sin(180-A-C)=sin(A+B=sinAcosB+sinBcosA 3sinA+4cosB=6,4sinB+3cosA=1两式举碧分闷知别平方相加得9sinA^2+16cosB^2+24sinAcosB+16sinB^2+9cosA^2+24sinBcosA=37sinA^2+cosA^2=1,sinC=1/2 ,C=30度