sinA+sinC=2sin[(A+C)/2]×cos[(A-C)/2]=2sin[(π-B)/2]×cos(π/6)=2sin(π/2-B/2)×√3/2=√3cos(B/2)=√3×(1+cosB)/2.已知sinA+sinC=2sinB,则：√3×(1+cosB)/2=2sinB化简得：cosB=4√3sinB/3-1,将等式两边平方...