∵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 = 2π/3,B+C=π/3
而sinB+sinC = 2sin[(B+C)/2]·cos[(B-C)/2] = cos[(B-C)/2],∵0
∵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 = 2π/3,B+C=π/3
而sinB+sinC = 2sin[(B+C)/2]·cos[(B-C)/2] = cos[(B-C)/2],∵0