∵向量m∥向量n,∴cosB、cosA均不为0,且-cosB/cosA = (2c+b)/a = (2sinC+sinB)/sinA∴-sinAcosB = 2sinCcosA + sinBcosA ,∴2sinCcosA + sin(A+B) = 0 = sinC·(1 + 2cosA)∵C是内角,∴sinC≠0,∴cosA = -1/2,A = 2...