只有当C=90°时,才成立 (sinA + sinB)/sinC = (sinA + sin(90°-A))/sin90° = (sinA + cosA)/1 = sinA + cosA 当C≠90°时,不成立 例如A=B=C=60° (sinA + sinB)/sinC=2 sinA+cosA=(1+√3)/2
