On the Poisson integral formula for the upper half plane












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I was trying to derive the Poisson formula for the upper half plane. However, I got stuck and found this Derive the Poisson Formula for a bounded C-harmonic function in the upper half-plane.
Now I am not able to prove the inequality $|(zeta - z)(zeta -overline{z})|>frac{1}{2}R^2$ which is required as per the answer by @mrf. I think its simple and straightforward but somehow I am missing out something. It will be really helpful if someone can provide me the details. Thanks in advance.










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  • 1




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    $z$ is fixed in the upper half-plane and $zeta$ is on the disk of radius $R$ so $|zeta-z|^2 ge (R-|z|)^2$, that's all you need.For $R$ large enough $(R-|z|)^2ge frac{R^2}{2} $
    $endgroup$
    – reuns
    Jan 20 at 2:13












  • $begingroup$
    @reuns Thanks. I got it.
    $endgroup$
    – Himadri Karmakar
    Jan 20 at 3:38
















1












$begingroup$


I was trying to derive the Poisson formula for the upper half plane. However, I got stuck and found this Derive the Poisson Formula for a bounded C-harmonic function in the upper half-plane.
Now I am not able to prove the inequality $|(zeta - z)(zeta -overline{z})|>frac{1}{2}R^2$ which is required as per the answer by @mrf. I think its simple and straightforward but somehow I am missing out something. It will be really helpful if someone can provide me the details. Thanks in advance.










share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    $z$ is fixed in the upper half-plane and $zeta$ is on the disk of radius $R$ so $|zeta-z|^2 ge (R-|z|)^2$, that's all you need.For $R$ large enough $(R-|z|)^2ge frac{R^2}{2} $
    $endgroup$
    – reuns
    Jan 20 at 2:13












  • $begingroup$
    @reuns Thanks. I got it.
    $endgroup$
    – Himadri Karmakar
    Jan 20 at 3:38














1












1








1





$begingroup$


I was trying to derive the Poisson formula for the upper half plane. However, I got stuck and found this Derive the Poisson Formula for a bounded C-harmonic function in the upper half-plane.
Now I am not able to prove the inequality $|(zeta - z)(zeta -overline{z})|>frac{1}{2}R^2$ which is required as per the answer by @mrf. I think its simple and straightforward but somehow I am missing out something. It will be really helpful if someone can provide me the details. Thanks in advance.










share|cite|improve this question









$endgroup$




I was trying to derive the Poisson formula for the upper half plane. However, I got stuck and found this Derive the Poisson Formula for a bounded C-harmonic function in the upper half-plane.
Now I am not able to prove the inequality $|(zeta - z)(zeta -overline{z})|>frac{1}{2}R^2$ which is required as per the answer by @mrf. I think its simple and straightforward but somehow I am missing out something. It will be really helpful if someone can provide me the details. Thanks in advance.







complex-analysis






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share|cite|improve this question











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asked Jan 19 at 16:21









Himadri KarmakarHimadri Karmakar

1419




1419








  • 1




    $begingroup$
    $z$ is fixed in the upper half-plane and $zeta$ is on the disk of radius $R$ so $|zeta-z|^2 ge (R-|z|)^2$, that's all you need.For $R$ large enough $(R-|z|)^2ge frac{R^2}{2} $
    $endgroup$
    – reuns
    Jan 20 at 2:13












  • $begingroup$
    @reuns Thanks. I got it.
    $endgroup$
    – Himadri Karmakar
    Jan 20 at 3:38














  • 1




    $begingroup$
    $z$ is fixed in the upper half-plane and $zeta$ is on the disk of radius $R$ so $|zeta-z|^2 ge (R-|z|)^2$, that's all you need.For $R$ large enough $(R-|z|)^2ge frac{R^2}{2} $
    $endgroup$
    – reuns
    Jan 20 at 2:13












  • $begingroup$
    @reuns Thanks. I got it.
    $endgroup$
    – Himadri Karmakar
    Jan 20 at 3:38








1




1




$begingroup$
$z$ is fixed in the upper half-plane and $zeta$ is on the disk of radius $R$ so $|zeta-z|^2 ge (R-|z|)^2$, that's all you need.For $R$ large enough $(R-|z|)^2ge frac{R^2}{2} $
$endgroup$
– reuns
Jan 20 at 2:13






$begingroup$
$z$ is fixed in the upper half-plane and $zeta$ is on the disk of radius $R$ so $|zeta-z|^2 ge (R-|z|)^2$, that's all you need.For $R$ large enough $(R-|z|)^2ge frac{R^2}{2} $
$endgroup$
– reuns
Jan 20 at 2:13














$begingroup$
@reuns Thanks. I got it.
$endgroup$
– Himadri Karmakar
Jan 20 at 3:38




$begingroup$
@reuns Thanks. I got it.
$endgroup$
– Himadri Karmakar
Jan 20 at 3:38










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