1、正弦定理：a/sinA=b/sinB=c/sinC 变形:1,a/c=sinA/sinC a/b=sinA/sinC b/c=sinB/sinA 2,a/b/c=sinA/sinB/sinC 3,a=2R*sinA b=2R*sinB c=2R*sinC 4,sinA=a/2R sinB=b/2R sinC=c/2R 5,A＜B=a＜b=2R*sinA＜2R*sinB=sinA＜sinB。