An almost reverse triangle inequality involving two complex numbers

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Given two complex numbers $u$ and $v$, numerically it seems that
$$1+vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert u+vvert+vert 1+u+vverttag$*$$$
with equality holding for example when $(u=v=-1)$ Or $(u=exp(frac2ipi3),v=exp(frac4ipi3))$ but these are not the only cases.



This inequality does not follow in a clear way to me from Hlawka's inequality, but it looks some how similar to a difficult inequality
$$vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert1+uvvert$$
which was proved in this paper.



I would appreciate any idea or help in proving $(*)$.










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    up vote
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    favorite
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    Given two complex numbers $u$ and $v$, numerically it seems that
    $$1+vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert u+vvert+vert 1+u+vverttag$*$$$
    with equality holding for example when $(u=v=-1)$ Or $(u=exp(frac2ipi3),v=exp(frac4ipi3))$ but these are not the only cases.



    This inequality does not follow in a clear way to me from Hlawka's inequality, but it looks some how similar to a difficult inequality
    $$vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert1+uvvert$$
    which was proved in this paper.



    I would appreciate any idea or help in proving $(*)$.










    share|cite|improve this question

























      up vote
      6
      down vote

      favorite
      5









      up vote
      6
      down vote

      favorite
      5






      5





      Given two complex numbers $u$ and $v$, numerically it seems that
      $$1+vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert u+vvert+vert 1+u+vverttag$*$$$
      with equality holding for example when $(u=v=-1)$ Or $(u=exp(frac2ipi3),v=exp(frac4ipi3))$ but these are not the only cases.



      This inequality does not follow in a clear way to me from Hlawka's inequality, but it looks some how similar to a difficult inequality
      $$vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert1+uvvert$$
      which was proved in this paper.



      I would appreciate any idea or help in proving $(*)$.










      share|cite|improve this question















      Given two complex numbers $u$ and $v$, numerically it seems that
      $$1+vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert u+vvert+vert 1+u+vverttag$*$$$
      with equality holding for example when $(u=v=-1)$ Or $(u=exp(frac2ipi3),v=exp(frac4ipi3))$ but these are not the only cases.



      This inequality does not follow in a clear way to me from Hlawka's inequality, but it looks some how similar to a difficult inequality
      $$vert uvert +vert vvertle vert 1+uvert +vert 1+vvert+vert1+uvvert$$
      which was proved in this paper.



      I would appreciate any idea or help in proving $(*)$.







      complex-analysis inequality






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      edited Feb 2 at 6:07

























      asked Jan 24 at 11:00









      Omran Kouba

      23.7k13579




      23.7k13579




















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          This follows from Hlawka. Denormalizing the inequality, you want to show
          $$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
          Substitute $u = y+z, v = z+x, w = x+y$, you want to show
          $$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
          But Hlawka tells you that
          $$beginalign*
          textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
          &= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
          &ge |v+w-u| + |w+u-v| + |u+v-w| \
          &= textLeft hand side
          endalign*$$






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            1 Answer
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            active

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            1 Answer
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            active

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            active

            oldest

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            up vote
            4
            down vote



            accepted










            This follows from Hlawka. Denormalizing the inequality, you want to show
            $$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
            Substitute $u = y+z, v = z+x, w = x+y$, you want to show
            $$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
            But Hlawka tells you that
            $$beginalign*
            textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
            &= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
            &ge |v+w-u| + |w+u-v| + |u+v-w| \
            &= textLeft hand side
            endalign*$$






            share|cite|improve this answer


























              up vote
              4
              down vote



              accepted










              This follows from Hlawka. Denormalizing the inequality, you want to show
              $$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
              Substitute $u = y+z, v = z+x, w = x+y$, you want to show
              $$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
              But Hlawka tells you that
              $$beginalign*
              textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
              &= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
              &ge |v+w-u| + |w+u-v| + |u+v-w| \
              &= textLeft hand side
              endalign*$$






              share|cite|improve this answer
























                up vote
                4
                down vote



                accepted







                up vote
                4
                down vote



                accepted






                This follows from Hlawka. Denormalizing the inequality, you want to show
                $$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
                Substitute $u = y+z, v = z+x, w = x+y$, you want to show
                $$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
                But Hlawka tells you that
                $$beginalign*
                textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
                &= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
                &ge |v+w-u| + |w+u-v| + |u+v-w| \
                &= textLeft hand side
                endalign*$$






                share|cite|improve this answer














                This follows from Hlawka. Denormalizing the inequality, you want to show
                $$|x| + |y| + |z| leq |x+y| + |y+z| + |z+x| + |x+y+z|$$
                Substitute $u = y+z, v = z+x, w = x+y$, you want to show
                $$|v+w-u| + |w+u-v| + |u+v-w| leq 2(|u| + |v| + |w|) + |u+v+w|$$
                But Hlawka tells you that
                $$beginalign*
                textRight hand side &ge (|u| + |v| + |w|) + (|u+v| + |v+w| + |w+u|) \
                &= (|v+w| + |u|) + (|w+u| + |v|) + (|u+v| + |w|) \
                &ge |v+w-u| + |w+u-v| + |u+v-w| \
                &= textLeft hand side
                endalign*$$







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                edited Sep 9 at 15:50

























                answered Sep 9 at 5:44









                Pig

                206113




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