令pq夹角为x ,则向量积 = p的模·q的模·cosx = 1·1·cosπ/3 = (cosb/2)·(cosb/2) + (sinb/2)·(-sinb/2) = (cosb/2)^2 - (sinb/2)^2 = cosb ,即cosb = cosπ/3 ,又∵B是三角形内角 ,∴B = π/3由tanC =√3/2 >√...