若角a,b满足-π/2若角a,b满足-π/2若角a,b满足-π/2-π/2所以-π/2<-b<π/2-π/2所以-π<2a<π相加-3π/2<2a-b<3π/2
若角a,b满足-π/2-π/2所以-π/2<-b<π/2-π/2所以-π<2a<π相加-3π/2<2a-b<3π/2