已知集合A={X|a①当2a+1<a即a<-1时,A为空集.②当2a+1≥a即a≥-1时,有:2a+1<-1或a≥2即a<-1或a≥2综上所述,a<-1或a≥2
①当2a+1<a即a<-1时,A为空集.②当2a+1≥a即a≥-1时,有:2a+1<-1或a≥2即a<-1或a≥2综上所述,a<-1或a≥2