a+c=2b∴sinA +sinC = 2sinB2sin[(A+C)/2] * cos[(A-C)/2] = 2sinBsin[(A+C)/2] * cos(π/6) = sinB因为A + B + C = π所以：(A+C)/2 = π/2 - B/2cos(B/2) * √3/2 = 2sin(B/2)cos(B/2)显然B/2不等于π/2,cos(B/2)...*这个是什么意思？....乘号